Correct is A.

What do you need to use 'Update ld;' when you are on before update trigger

Correct answer is A

Answer is C :

In Apex, a compile-time exception refers to an error that is detected by the compiler during the compilation of your code. These errors prevent the code from being compiled into an executable form. They are typically caused by syntax errors, type mismatches, or other issues that the compiler can detect without executing the code.

Answer is C, surely this is a compile exception (comma here: trigger.old,ap.get)