The Substring method is used to extract a part of a string based on a specified starting index and length. The syntax of the Substring method is:
string.Substring(startIndex, length)
where startIndex is the zero-based position of the first character in the substring, and length is the number of characters in the substring. For example, if the string is "Hello", then string.Substring(1, 2) will return "el", as it starts from the second character (index 1) and takes two characters.
To return four characters starting with the second character, the startIndex should be 1 and the length should be 4. Therefore, the expression should be:
StrVar.Substring(1, 4)
References: Substring and How to manipulate a part of string: Split, Trim, Substring, Replace, Remove, Left, Right from UiPath documentation and forum.

To change the profile from UiPath Studio to UiPath StudioX, a user needs to go to Home, then Settings, select License and Profile, choose Change Profile, and click on the UiPath StudioX profile. After that, the user must confirm the profile change and agree to restart the application for the changes to take effect. Thus, the correct answer is C.
References:
UiPath Studio Guide: Switching Between Profiles

The Strict Selector option allows you to fine-tune the selector by adjusting the accuracy level and showing all the matches in the UI Explorer. The other options are not available at indication time.
References:
* Selectors in UiPath Studio course, Lesson 3: UI Explorer, Topic: Strict Selector
* Uipath Associate Certification UiRPA Question Latest course, Section 2: UI Automation, Lecture:
Question 10

This is because the code is throwing a new IOException, but there is no catch block defined for IOException.
The catch blocks present are for BusinessRuleException, ArgumentException, and InvalidOperationException. Therefore, the code will not be able to handle the thrown exception. References:
https://docs.uipath.com/activities/docs/try-catch