填入下面横线上的话，与上下文衔接最恰当的一项是(　　)事实上，凡优秀的文艺作品，________因此它们才能成为生活的教科书，成为生活的良师益友。

With so many people ______ around her, the girl felt very nervous and grasped her mother’s hand tightly.

e _______ the door, he foundhis keys were nowhere

_______ caused the accident is still a completemystery.

Where did you see your friend—It was in the super market ____ I was doing shopping