Ответ:
1) Rivers flows forwards the sea.
Rivers doesn't flow forwards the sea.
2) A student buys a lot of books at the beginning of each term.
A student does't buy a lot of books at the beginning of each term.
3) The students are taking a test in class right now.
The students are not taking a test in class right now.
4) Music makes me forget my problems.
Music doesn't make me forget my problems.
5) The lecturer is explaining something to them an the moment.
The lecturer isn't explaining something to them an the moment.
Объяснение: