"In China, waste is growing twice as fast as the population," the lecturer said.

A. Trees, which should be planted everywhere possible, absorb carbon dioxide, a greenhouse gas.

B. Trees should be planted everywhere possible as they absorb carbon dioxide, a greenhouse gas.

C. Trees should be planted everywhere possible to be able to absorb carbon dioxide, a greenhouse gas.

D. Trees should be planted everywhere possible where they absorb carbon dioxide, a greenhouse gas.

A. Biodiversity has its own economic importance, so protection of biodiversity is important.

B. Biodiversity has its own economic importance that protection of biodiversity is important.

C. Protection of biodiversity is so important that biodiversity has its own economic importance.

D. Protection of biodiversity is important to make biodiversity have its own economic importance.

A. We will not know where all our rubbish goes.

B. We should know where all our rubbish goes.

C. We did not know where all our rubbish goes.

D. We will never know where all our rubbish went.

A. He said his girlfriend that he had bought a ring.

B. He said his girlfriend that he bought a ring.

C. He told his girlfriend that he had bought a ring.

D. He told his girlfriend that he bought a ring.

A. Emily said that we were staying in tonight.

B. Emily said that they were staying in tonight

C. Emily said that we were staying in that night.

D. Emily said that they were staying in that night.

A. Many wonder what happens to what we throw away.

B. Many wondered what happened to what we threw away.

C. Many wondered what has happened to what we threw away.

D. Many wonder what happened to what we threw away.