HE/ HELP/ HIS FRIEND/ GET GOOD MARK/ EXPLAIN/ LESSONS/ CAREFULLY//...

50. He/ help/ his friend/ get good mark/ explain/ lessons/ carefully//He helped his friend get good mar-k by explaining the lessons carefully.B. Read the passage carefully, then choose the correct answer.In an early survey conducted in 1888, a billion and a half peopleinhabited the earth. Now, the population is about six billion and is growingfast. Even though the rate of growth has begun to slow down, most peoplebelieve the population size may be eight billion during the next several years.If we examine the amount of land available for this ever increasingpopulation, we begin to see the problem. Not all land is useful to us becauseit cannot produce food. We can cut out about one fifth of it because it iscovered by snow and ice. Then we can cut out another fifth because it isdesert. Another fifth is mountains. The other fifth does not have enough soilfor crops to grow because it is bare rock. Obviously, with so little land tosupport us, we should take great care not to reduce it any more or with therapidly growing population we may sooner or later lack food to eat and placeto live in.