The correct option is A to what was to be the Treaty of Utrecht was not to be signed until September 1711, and the final treaty in March 1713, but the peace process started moving
Firstly agreement of.. is incocrrect, so options (D) and (E) are wrong. Usually agreement of is used in the title of an agreement such as Agreement of Sales
Now lets look why (B) and (C) are wrong:
(B) to what was to be the Treaty of Utrecht was not to be signed until September 1711, but the peace process started to move before the final treaty in March 1713 Read this with the last part of the sentence, it gives, ...before the final treaty in March 1713 before the end of 1710. Seems senseless. Hence wrong.
(C) to what was the Treaty of Utrecht was not signed until September 1711, and the final treaty in March 1713, but the peace process had started to move Changes the meaning of the sentence. It means that the agreement to what was (not what it will be) the Treaty of Utrecht was actually the one that was not signed until 1711. Also introduces a tense error. Hence wrong
(A) to what was to be the Treaty of Utrecht was not to be signed until September 1711, and the final treaty in March 1713, but the peace process started moving. Now lets look at option A. It is clear that the agreement to what was to be the Treaty should not be signed until Sept 1711 and the final treaty in March 1713. However, the peace process for the same started moving before the end of 1710. Clear and concise.