Nobody but us _____ the secret.
| A．know | B．knows | C．have known | D．is known |
．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 |
—Does_____please you to give gifts to others?
—Sure．
| A．it | B．that | C．one | D．he |
He didn’t make_______clear when and where the meeting would be held.
| A．this | B．that | C．it | D．these |