This question is based on several suppositions:
For as a preposition is able to be transformed into a wh- question with the wh- phrase preposed with for, as below with senators John acting as the complement:
1 (a) I will vote for Senator John in the election. (b) For which senator will you vote in the elections?
However, in 2(a) below, Senator John only is not the complement of for. Instead, for is a complementiser for the clause Senator John to keep his cool. Senator John being the subject of the expression to keep his cool, the wh-expression can’t be preposed with for:
2 (a) They were anxious for Senator John to keep his cool. (b) * For which senator were they anxious to keep his cool?
When for functions as a complement, the whole for clause can often be substituted with a that clause, but the prepositional for phrase can’t be replaced by a that clause:
3 (a) Is it really necessary for there to be a showdown? (b) Is it really necessary that there (should) be a showdown?
4 (a) We are heading for a general strike. (b) * We are heading that there (will) be a general strike.
Given the above, in which of the following sentences could for be either a complementiser or a preposition:
A. The dog went straight for her throat.
B. It is important for parents to spend time with their children.
C. We are hoping for a peace agreement to be signed.
The expected answer is B because it passes both the preposing wh-expression with for test (For whom is it important to spend time with their children?) and the complementiser test of replacing for with that (It is important that parents spend time with their children.
My question is: Can anyone explain why C does not pass the preposition test? It passes the complement test (We are hoping that a peace agreement be signed) but not the preposition test (For which agreement/what are we hoping to be signed?). Is this for which expression actually incorrect?
I have a bunch of ideas on this, but don’t to further muddle this already complicated post.
Thanks in advance for any contributions!!