The discovery of the new drug is of great ____ to people who suffer from heart problems.
| A．appreciation | B．significance | C．satisfaction | D．guidance |
Scientists are convinced ___ the positive effect of laughter ___ physical and mental health.
| A．of; at | B．by; in | C．of; on | D．on; at |
We had to wait half an hour _______ we already booked a table.
| A．since | B．although | C．until | D．before |
Help others whenever you can ______ you will make the world a nicer place to live in.
| A．and | B．or | C．unless | D．but |
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 |
___ the silence of the pauses, we could hear each other’s breathing and could almost hear our own heartbeats.
| A．In | B．For | C．Under | D．Between |