The keyword here is "endpoint". The only two items related to endpoint is secure boot and USB port restriction.

B is correct answer.

From wikipedia,

The attack surface of a software environment is the sum of the different points (for "attack vectors") where an unauthorized user (the "attacker") can try to enter data to or extract data from an environment.[1][2] [3]Keeping the attack surface as small as possible is a basic security measure.

The only problem here is that Social Engineering is not a "testing method" it is an attack.

But the other alternatives are wrong, so (A) is correct.

Social engineering attacks leverage the weakest link, which is the human user. If the attacker can get the user to reveal information, it is much easier for the attacker to cause harm rather than use some other method of reconnaissance. This could be done through email or misdirection of web pages, which results in the user clicking something that leads to the attacker gaining information. Social engineering can also be done in person by an insider or outside entity or over the phone.

From the book:

Other social engineering techniques include the following: Phishing, Spear phishing, Pharming (is the term used to describe a threat actor redirecting a victim from a valid website or resource to a malicious one that could be made to appear as the valid site to the user. From there, an attempt is made to extract confidential information from the user or to install malware in the victim’s system. Pharming can be done by altering the host file on a victim’s system, through DNS poisoning, or by exploiting a vulnerability in a DNS server.), Malvertising, SMS phishing, Voice phishing (or vishing), Whaling, Elicitation, interrogation, and impersonation (Pretexting)

"B" is correct.

A certificate authority is a computer or entity that creates and issues digital certificates.

CA do not "authenticate" it validates.

"D" is wrong because The digital certificate validate a user.

CA --> DC --> user, server or whatever.

C is correct answer.

Cipher suite is just a set of available ciphers that can be used by a device for encryption.

B is correct.

Protocol 41 is a communication protocol which embeds internet protocol version 6 (IPv6) packets inside Internet protocol version 4 (IPv4) packets.

D is correct answer.

Cyber Threat Defense with NetFlow

C - correct check cyber ops by Omar Santos page; 836