单选题 (Only then)(he became) aware of (the fact) that there were more difficulties ahead (than) he had expected.
【正确答案】 B
【答案解析】改为didhebecome．Only放于句首且加副词时，后面句子要用倒装语序。本句意思是：直到那时他才意识到有着比原来想象中更多的困难。