—Are you free tomorrow afternoon?
—I'm afraid not. I'll have to __________ an important lecture given by a famous professor.
| A．join | B．take part in |
| C．attend | D．enter |
They were walking along the shore _______ a huge wave appeared out of nowhere, sweeping them out to sea.
| A．as | B．while | C．when | D．though |
_______, and the problem will be straightened out.
| A．There being a little effort | B．Having a little effort |
| C．If you have a bit more effort | D．A bit more effort |
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 |