since this is an assumption type of question, the correct answer should present new information that is in the scope of the passage and that if negated, the conclusion would shatter.
(A) The United States has a larger voting share of the Intercontinental Bank than does China or Belgium.
the argument is not concerned with the fact that US has more voting shares. OFS.
(B) The specific allocation of voting shares factors into the Intercontinental Bank's effectiveness in shaping global economic policy.
if this is not true, then the argument that since C has 15% of WGDP is irrelevant, and cannot be used as an premise to support the conclusion that the voting shares should be changed. looks good so far.
(C) Only voting shares that are precisely proportional to each country's contribution to the global economy are appropriate for the Intercontinental Bank.
which shares are appropriate for the IC is irrelevant and out of scope.
(D) The Intercontinental Bank is necessary to the maintenance of a prosperous global economy.
while it might be true, the author does not assume that.
(E) As one of the fastest growing economies, China should have a larger voting share in the Intercontinental Bank.
this might be something inferred from the argument. Since inferred information cannot be the assumption, E is not correct.
after POE, the only answer choice that looks good is B.