Question

Paul thinks he`s very busy this week. 改为否定句

Answer 1

Paul doesn't think he is very busy this week 。

这是否定前移。
否定前移的句子主语必须是第一人称。另外还有两个条件：一是主句的时态必须为一般现在时，二是主句的动词必须是think/believe/suppose/expect等。如果上述三个条件有一个不符合，就不能称之为否定前移。
2）主从复合句如全部符合上述条件，就必须把宾语从句的否定前移至主句，而不能否定宾语从句。
3）当然如果不符合上述条件，那这时句子的否定放在主句或从句都是可以的，只不过它不管怎样放置，就都不能算是否定前移的语法现象了。

Answer 2

Paul doesn't think he is very busy this week

Answer 3

Paul doesn't think he`s very busy this week

Answer 4

Paul doesn't think he`is very busy this week.

Answer 5

Paul doesn't think he is very busy this week