They took a long time to finish the work because (a) they were very tired.
PASSAGE
We started pitching the highest camp that has ever been made. Everything took five times as long as it would have taken in a place where there was enough air to breathe; but at last we got the tent up, and when we crawled in, it was not too bad. There was only a light wind, and inside it was not too cold for us to take off our gloves. At night most climbers take off their boots; but I prefer to keep them on. Hillary, on the other hand, took his off and laid them next to his sleeping bag.
They took a long time to finish the work because
(a) they were very tired.
(b) there was not enough air to breathe.
(c) it was very cold.
(d) it was very dark.
1 Answers
(b) They took a long time to finish the work because there was not enough air to breathe at such a high altitude.
All the other three options (a), (c) and (d) are true, but they are not clearly stated in the passage as in the case of option (b).