Remark
Be very careful how many parts you post to a question.
15
The answer is between C and D. Historically people did think parts of it must have been beautiful. It is 215 miles long!! There must be parts of it that are rural and quite beautiful. All rivers have a beauty to them. Not very many hoards really tried to come up the river to make an invasion against London. The answer is D. That 215 miles is a huge distance and it lends itself very well to commerce.
16
London has a very large population. Millions of people dumping refuge into a river would sure get someone's attention. I think the obvious answer is C. A is a tempting answer, but where would they go? Pick C
17
D is indirect and not very much. Fish exhale oxygen, that not enough to make any difference to the atmosphere. Also trees along the banks would also produce oxygen but again not a significant amount.
Up stream you might find grain harvesting, but other parts of England would do better.
Light to see with is just an answer to make 4. It might be right, but it's not relevant.
Always think transportation. A is what you should pick.
18
There i no other answer but D.
A would overlook the pollution
B Recreation does not equal pollution problems of a river. Recreation might contribute to the pollution problems of a river, but that is not your best answer.
C You could do that, but D is more to the point. C is the second best answer.
