How to use 'as well as' and 'even'?

When I was doing my English homework, I came across this question:

In his research paper Dr Brown suggests that snacking, if done properly, makes people healthier and __ helps control weight.
A. as well as       B. namely       C. even       D. yet

I chose A, but my tutor said the correct answer should be C. But she did not give me a satisfactory explaination. Could you kindly tell me why I can't use as well as in this sentence?

In his research paper Dr Brown suggests that snacking, if done properly, makes people healthier and as well as helps control weight.

This is incorrect because as well as is a conjunction, so it doesn't make sense after and has already been used to join the two clauses. It would be correct to use as well as if and were not present.

In his research paper Dr Brown suggests that snacking, if done properly, makes people healthier and namely helps control weight.

Namely is used to provide a single example to be more specific about what you've already mentioned. It would be correct if you were to write, for example:

Snacking, if done properly, makes people healthier: namely, it helps control weight.

Both even and yet are grammatically fine in this context, but you're trying to add emphasis (even), not introduce a contradiction (yet). Yet doesn't make sense because helping control weight is related to making people healthier, not in opposition to it. An example where yet would make sense:

In his research paper Dr Brown suggests that snacking, if done properly, makes people healthier and yet I still don't believe it.