Also we know that astronauts, when they go up into space, find the air becomes ________(thin)as they go higher.

How can we achieve specific reference (with examples)?

What are principles governing the subject-verb concord? Give your answer with examples.

Using whatever cohesive device is appropriate:

John was the winner in 1999, and Bob was the winner in 2000.

Using whatever cohesive device is appropriate:

The production increases as it has increased for the last few years.

Using subjunctive mood:

It suffices to say that the open policy will remain unchanged.

Using a modal auxiliary:

It’s possible that our team will win the race.

Using discontinuity:

Many forms of apparatus by which a more accurate knowledge of blood pressure can be obtained have been devised.

Using inversion:

He had hardly finished his work when the telephone rang.

Combining the two sentences by using a conjunct:

He is being a fool. He is behaving foolishly.

Using a disjunct:

I will say frankly that I was rather impressed by his manner.