The correct answer is c. Everything seems like a struggle when you are suffering from depression.
The word everything is considered to be third person singular, which means that the verb has to end in -s in the present simple form. This is why D is incorrect. A is incorrect because somebody is also considered to be third person singular, which means that the verb next to it should be 'seems.' B is incorrect because many is plural, which means that the verb cannot have the suffix -s, but rather be just 'suffer.'