---How amazing it is that astronauts are exploring outer space！
---It’s a challenge, I guess, man against nature.
| A．of |
| B．for |
| C．by |
| D．about |
．—When can we come to visit you?
—Anytime you feel like________.
| A．one | B．it | C．so | D．that |
Really great people always see the best in others; it is the little man who looks for the worst and finds_________.
| A．one | B．it | C．that | D．them |
．No one knows exactly when our ancestors started talking，but new evidence suggests _______might have happened a long time ago．
| A．which | B．what | C．it | D．they |
．—Do you think_____ worthwhile to go all the way to Los Angles to buy that computer?
—Well ,I’m going to visit some relatives, too.
| A．it | B．/ | C．this | D．that |
Though we found _____difficult to avoid economic and financial crisis, we must take measures to reduce its negative impact.
| A．it | B．one | C．that | D．how |