Ihave a mountain of bills piling up on my desk. what figure of speech is it?

The figure of speech in this sentence is a hyperbole.

'Mountain of bills' is an exaggeration to strongly point out something. It doesn't have to be taken literally. These kinds of sentences create strong impressions or feelings by exaggerating a word or phrase in the sentence.

You cannot take this extravagant statement literally, as it does not provide any concrete meaning. It is present in the sentence to only emphasize on the incident strongly.

the two answers are

get thee back into the tempest and the night's plutonian shore

on the pallid bust of pallas just above my chamber door

answer: this is not a good thesis statement because a thesis statement is not supposed to have questions in it. a thesis states your position on your topic. a question cannot state anything because it is not a statement. a question is a great lead in to a thesis, but it can't be the thesis.