Write the verb in brackets in the correct form. The United Nations (to have) meetings where world leaders agree on what to do about global warming. If there is too much pollution in the air, some people (to have) health problems.

Ecologists looked for special spots on white pine trees to know if there
(to be) high levels of ozone.

Many types of air pollution are invisible, but some can (to see) with the naked eye.

The teacher asked the boys if they (to do) the task.

Satellite images proved that deforestation
(to increase) rapidly.

The passage is so difficult that I (can) understand it.

Experts said that less than 3 per cent of the water on Earth (to be) fresh water.

His health has improved since he (to return) from the hills.

If we had sorted the waste, we (to save) millions of kilowatts of energy.​

The United Nations had meetings where world leaders agree on what to do about global warming. If there is too much pollution in the air, some people had 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 saw 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 could 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 sawed millions of kilowatts of energy.​

Объяснение:

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.​

foreign languages are necessary for everybody in modern society. it helps us to make friends from other countries and communicate with them without any problems,it helps us in travelling,in using the internet resources for getting more information.speaking foreign language helps us to earn more money.

we all have to learn ,to do our best in learning languages as it helps to be more successful

1)christmas

2)week

3)second