_________ is known to all，good friends _________ happiness and value to life.
| A．It； add | B．As； add | C．It； add up | D．As； add to |
Water, which seems so simple and common, is _____ makes life possible.
| A．that | B．what | C．which | D．how |
_____ is no possibility that Bob can win the first prize in the match.
| A．There | B．It | C．That | D．This |
—Have you ever ridden a horse ?
—No, but I _____ a camel when I visited Egypt last year.
| A．was riding | B．have ridden | C．rode | D．had ridden |
—I must apologize for ________ ahead of time.
—that’s all right.
| A．letting you not know | B．not letting you know |
| C．letting you know not | D．letting not you know |
________ I understand you，I still can’t support you.
| A．When | B．After | C．While | D．As |