填在下面横线上最恰当的一项是 （ ）____ 崖壁下有几处坟地，坟前立着石碑，许多已经破碎，字迹模糊；枯水季节，伏在江里的石头有的已经露出水面，周围一片寂静。

I’ll ask the teacher about past tense. I’m very puzzled about it. — That is just _____ most of our classmates have doubt.

He hardly ever feels tired, ______

Do you hear a fire ___ last night?—Yes, it __ by the firemen in no time.

When do you usually in the morning—That depends on what time my alarm clock goes off!