Isolation is the first step to take after detecting some indicators of compromise (IoCs) of possible ransomware contamination. Isolation prevents the ransomware from spreading to other servers or segments of the network, and allows the security team to investigate and contain the incident. Isolation can be done by disconnecting the infected servers from the network, blocking the malicious traffic, or applying firewall rules12.
References: 10 Things You Should Do After a Ransomware Attack, How to Recover from a Ransomware Attack: A Step-by-Step Guide

The security analyst is validating a Local File Inclusion (LFI) vulnerability, as indicated by the "/.../.../.../" in the GET request which is a common indicator of directory traversal attempts associated with LFI. The other options are not relevant for this purpose: SQL injection involves injecting malicious SQL statements into a database query; XSS involves injecting malicious scripts into a web page; CSRF involves tricking a user into performing an unwanted action on a web application.
References: According to the CompTIA CySA+ Study Guide: Exam CS0-003, 3rd Edition1, one of the objectives for the exam is to "use appropriate tools and methods to manage, prioritize and respond to attacks and vulnerabilities". The book also covers the usage and syntax of Burp Suite, a tool used for testing web application security, in chapter 6. Specifically, it explains the meaning and function of each component in Burp Suite, such as Repeater, which allows the security analyst to modify and resend individual requests1, page 239. Therefore, this is a reliable source to verify the answer to the question.

The activities taken by the process with PID 1024 will provide the best insight into this potentially malicious process, based on the anomalous behavior. BGInfo.exe is a legitimate tool that displays system information on the desktop background, but it can also be used by attackers to gather information about the compromised host or to disguise malicious processes. By monitoring the activities of PID 1024, such as the files it accesses, the network connections it makes, or the commands it executes, the analyst can determine if the process is benign or malicious.

Mean time to detect (MTTD) is a metric that measures how quickly an organization can identify a security incident or a malicious actor in the environment. Reducing MTTD can improve visibility and reporting of threats, as well as prevent lateral movement and data exfiltration by detecting them sooner.