The International Day against Drugs, aimed at warning people to keep away from drugs， _________ on June 26th every year．
| A．taking place | B．takes place | C．took place | D．taken place |
In that month, he earned as much as, if ____ than, $40 000.
| A．no more | B．not more | C．no much | D．not much |
The research is so designed that once _____ nothing can be done to change it.
| A．begins | B．having begun | C．beginning | D．begun |
If _____ carefully, the experiment will be successful.
| A．do | B．does | C．done | D．doing |
He is a man of few words, and seldom speaks until _____ to.
| A．spoken | B．speaking | C．speak | D．be spoken |
There are five pairs, but I'm at a loss which _____ to buy.
| A．to be chosen | B．to choose from | C．to choose | D．for choosing |