The domain name system (DNS) is the component that houses the MX record. The MX record is a type of DNS record that specifies which mail server is responsible for receiving email messages for a domain name.
VLAN is an acronym for virtual local area network, which is a logical subdivision of a network that allows devices to communicate as if they were on the same physical segment. DHCP is an acronym for dynamic host configuration protocol, which is a network protocol that assigns IP addresses and other configuration parameters to devices on a network automatically. SMTP is an acronym for simple mail transfer protocol, which is a network protocol that allows sending and receiving email messages over TCP/IP networks

If a computer is not booting and the onboard speaker emits beeps, it can indicate a hardware issue. One of the most common causes of beep codes is overheating, which can occur if the processor's fan is not properly installed and running. The processor's fan is responsible for cooling the processor and preventing damage to the internal components.

DDR3 is the most commonly used RAM type in modern desktop computers. It is faster and more energy efficient than its predecessors, and offers larger capacity modules. References: CompTIA A+ Certification Exam Guide, Ninth Edition, Chapter 5

To increase the performance of a laptop working with a large database stored on drive C, a systems administrator should increase the RAM and migrate to an SSD. Increasing the RAM will help the laptop to better handle the large database, while migrating to an SSD will improve the speed at which the laptop can access the database. Configuring RAID 1, installing a hybrid drive, upgrading to a 1GB NIC, and upgrading the power supply will not directly improve the laptop's performance when working with a large database.
References: CompTIA A+ Certification Exam: Core 1 - Objective 3.1

Lightning is a proprietary connection type that is used by Apple devices, such as iPhones, iPads, and iPods, to transfer data, charge, and connect to accessories. Lightning cables have a reversible 8-pin connector that can be plugged into a USB port on a workstation or a power adapter. USB-C, serial, and NFC are not compatible with Apple phones.
Reference: [CompTIA A+ Core 1 (220-1101) Certification Study Guide], page 13.