Does "amount" being singular/ plural depends on contextual usage ?

Example 1: Amount is Plural

Although the government's expenditures on law suits involving tobacco companies amounts to a sum dramatically lower than that spent by tobacco companies, many believe that the government should allocate no more funds to a battle they perceive as pointless.

(A) expenditures on law suits involving tobacco companies amounts to a sum dramatically lower than
(B) expenditures on law suits involving tobacco companies amount to a sum dramatically less than
(C) expenditures on law suits involving tobacco companies amount to a sum dramatically lower than
(D) law suit expenditures regarding tobacco companies amount to a dramatically lower sum than
(E) law suit expenditures against tobacco companies amounts to a sum dramatically lower than

Example 2: Amount is singular

While an extensive amount of research into the cause of acoustic neuromas have proven unsuccessful, doctors have developed new surgical options that have dramatically increased patients' survival rates

(A)amount of research into the cause of acoustic neuromas have proven unsuccessful

(B)amount of research into the cause of acoustic neuromas has proven unsuccessful

(C)quantity of research into the cause of acoustic neuromas have proven to be unsuccessful

(D)cause research into acoustic neuromas has proven unsuccessful

(E)amount of research has proven unsuccessful into the cause of acoustic
neuromas