Could you tell me how can I view the tutorial

About C, The idea is that at any moment, $$$x$$$ is always a multiple of $$$a$$$. So you just need to break $$$n$$$ into its prime factors $$$p_1, p_2, p_3,..., p_k$$$ where each $$$p_i$$$ is a prime and they don't need to be pairwise different. The answer for this problem is $$$1$$$ $$$+$$$ $$$p_1$$$ $$$+$$$ $$$p_2$$$ $$$+$$$ $$$...$$$ + $$$p_k$$$ $$$-$$$ $$$k$$$. I will leave the proof for you as an exercise.

For D, let's first check if the graph is already correct without the operator. Else, you must xor a non-empty set with some positive integer. If there exists edge of $$$u$$$ and $$$v$$$ and $$$a_u$$$ = $$$a_v$$$, then either $$$u$$$ or $$$v$$$ must be in the set. From here, the problem will become 2sat. To find suitable value so that it doesn't affect other edges, you can add every value of $$$a_u$$$ $$$xor$$$ $$$a_v$$$ to a set, and simply find the $$$mex$$$ of it.

Does the subarrays can change every year or the subarrays is unchangeable？

We are extremely sorry for that. I'll fix the statement.