John's success has nothing to do with good luck. It is years of hard work _______has made him a great scientist today.
| A．that |
| B．when |
| C．which |
| D．why |
Remember that you won't be able to cancel the contract ____you've signed.
| A．before | B．until | C．once | D．though |
Leonardo da Vinci (1452-1519) ____ birds kept in cages in order to have the pleasure of setting them free.
| A．is said to be buying | B．is said to have bought |
| C．had said to buy | D．has sad to have bought |
They paid fifty percent of _____ they were able to earn to the state．
| A．that | B．which | C．what | D．whom |
My sister is _______ about what she eats, otherwise she would not be so thin.
| A．special | B．curious | C．particular | D．specific |
I know a little bit about the city as I __________ there for one year in my youth.
| A．am studying | B．had studied | C．studied | D．have studied |