20% of the students of Nan Shan Senior High the school colorful clubs so far.
| A．has joined | B．has been joined |
| C．have joined | D．have been joined |
He______ on the grass, looking at the clouds in the sky.
| A．is laying | B．has laid | C．was lying | D．has lied |
The country life he was used to _______greatly since 1992.
| A．change | B．has changed | C．changing | D．have changed |
Most birds find it safe to sleep in the trees, but _______they have eggs or young chicks, they don’t use a nest.
| A．why | B．how | C．unless | D．where |
_______ boys and girls in that school are almost equal.
| A．A number of | B．The numbers of | C．Numbers of | D．The number of |
Every possible means ______to prevent the air pollution, but the sky is still not clear.
| A．is used | B．are used | C．have been used | D．has been used |