Write the verb in brackets in the correct form.
The United Nations (have) meetings where world leaders agree on what to do about global warming. If there is too much pollution in the air, some people (have) health problems.
Ecologists looked for special spots on white pine trees to know if there (were) high levels of ozone.
Many types of air pollution are invisible, but some can (be seen) with the naked eye.
The teacher asked the boys if they (had done) the task.
Satellite images proved that deforestation (was increasing) rapidly.
The passage is so difficult that I (can not) understand it.
Experts said that less than 3 per cent of the water on Earth (was) fresh water.
His health has improved since he (returned) from the hills.
If we had sorted the waste, we (would have saved) millions of kilowatts of energy.
The United Nations have meetings where world leaders agree on what to do about global warming. If there is too much pollution in the air, some people have health problems.
Ecologists looked for special spots on white pine trees to know if there
are any high levels of ozone.
Many types of air pollution are invisible, but some can be seen with the naked eye.
The teacher asked the boys if they did the task.
Satellite images proved that deforestation increased rapidly.
The passage is so difficult that I cannot understand it.
Experts said that less than 3 per cent of the water on Earth is fresh water.
His health has improved since he returned from the hills.
If we had sorted the waste, we would have saved millions of kilowatts of energy.
