Which pronoun correctly completes the elliptical clause? is everyone who works at this store as as
a. they
b. them

In colloquial English 'them" would be acceptable
In formal English 'they' is used accompanied by the corresponding auxilliary verb
So, you could  also say Is everyone who works in this store as helpful as they are ?

Ibelieve that the answer is d.

Because he is still kind of tired and needs something to rest on