Your #4 and #5 are correct. I have done #1 for you, and highlighted the mistakes in #2 and #3.
There areresearchers have found that optimists are more likely to succeed in life than pessimists, their direct opposites.
2. In the United States in the 1990, more than two-thirds of new jobs were temporary positions and these temporary workers make up more than 25 percent of the work force.
3. The stretch marks a woman gets after childbirth would not be there if she does not bring a new life into being.