Trees are useful to man mainly in three ways, the most important of which is that they can protect ______ from droughts (干旱) and floods.
| A．it | B．itself | C．himself | D．him |
The water will be polluted unless some measures _____.
| A．will be taken | B．are being taken | C．are taken | D．were taken |
His way of speaking suggested that he ____ very angry.
| A．should be | B．be | C．is | D．was |
Pine trees, of which there are almost one hundred _____, are found throughout the North Temperate Zone.
| A．species | B．samples | C．specimens | D．Standards |
The salmon dish was _______, wasn’t it?
| A．success | B．the success | C．a success | D．successes |
The conference had been held to discuss the effects of tourism ___ the wildlife in the rainforest.
| A．in | B．on | C． at |
D．with |