The most important part of a feasibility study is the economics1. A cost-benefit analysis of available products is crucial as it helps to understand the economic viability of the project1. It compares the costs of the project with the benefits it is expected to deliver, which is essential for making informed decisions1. Omitting this could lead to investments in hardware that may not provide the expected returns or meet the organization's needs.
References:
The Components of a Feasibility Study - ProjectEngineer

Encryption is the process of transforming information into an unreadable form using a secret key, so that only authorized parties can access it. Encryption would protect the confidentiality of information sent in email messages, as it would prevent unauthorized parties from intercepting and reading the messages. Secure Hash Algorithm 1 (SHA-1) is a cryptographic hash function that produces a fixed-length output from an input.
SHA-1 does not encrypt information, but rather verifies its integrity by detecting any changes or modifications. Digital signatures are electronic signatures that use encryption and hash functions to authenticate the identity of the sender and the integrity of the message. Digital signatures do not protect the confidentiality of information, but rather ensure its authenticity and non-repudiation. Digital certificates are electronic documents that contain the public key and identity information of an entity, such as a person, organization or device. Digital certificates are issued by trusted third parties called certificate authorities (CAs). Digital certificates do not protect the confidentiality of information, but rather enable secure communication and encryption by verifying the identity and public key of an entity. References:
* : [Encryption Definition]
* : [Secure Hash Algorithm 1 (SHA-1) Definition]
* : [Digital Signature Definition]
* : [Digital Certificate Definition]

The IS auditor should first determine whether the business impact analysis (BIA) is current with the organization's structure and context. The BIA is a critical component of the BCP and should reflect the current state of the organization. If the BIA is not up-to-date, it may not accurately reflect the impact of a disruption to the organization's operations, including the closure of a production plant12.
References: ISACA's Information Systems Auditor Study Materials1

Root cause is the most important thing for an IS auditor to determine and understand to develop meaningful recommendations for findings. A root cause is the underlying factor or condition that leads to a problem or issue. A finding is a statement that describes a problem or issue identified during an audit. A recommendation is a suggestion or advice that aims to address or resolve a finding. To develop meaningful recommendations for findings, an IS auditor should determine and understand the root cause of each finding, as this can help to identify the most effective and appropriate actions to prevent or correct the problem or issue. The other options are not as important as determining and understanding the root cause, as they do not directly address or resolve the finding. References: CISA Review Manual, 27th Edition, page 434

Data leakage prevention (DLP) is the process of preventing unauthorized access, disclosure, or transfer of sensitive data. In a multi-tenant cloud environment, where multiple customers share the same infrastructure and resources, DLP is a critical challenge. One of the best methods to enforce DLP in such an environment is to require tenants to implement data classification policies. Data classification policies define the types and levels of sensitivity of data, and the corresponding security controls and measures to protect them. By implementing data classification policies, tenants can ensure that their data is properly labeled, encrypted, segregated, and monitored according to their specific requirements and compliance standards. This can help prevent data leakage from accidental or malicious actions by other tenants, cloud service providers, or external parties.
References:
* 2: How Do I Secure my Data in a Multi-Tenant Cloud Environment? | Thales
* 3: Protecting Sensitive Customer Data in a Cloud-Based Multi-Tenant Environment | Saturn Cloud
* 4: Microsoft 365 isolation controls - Microsoft Service Assurance