Which of the following uses punctuation correctly to combine two sentences in the passage?
A. After four years of listening to speakers at school assemblies and graduations, it was his turn; he was ready.

B. After four years of listening to speakers at school assemblies and graduations: it was his turn; he was ready.

C. After four years of listening to speakers at school assemblies and graduations; it was his turn—he was ready.

D. After four years of listening to speakers at school assemblies and graduations—it was his turn—he was ready.