Anchor: For at least half of that time, those cells didn't have a nucleus.
Entailed: The cells do not have a nucleus for at least some of the time. 
Contradiction: All cells have a nucleus at all times. 
Contradiction: A natural environment at night is much noisier than most cities.
Contradiction: A man was looking through his telescope
Contradiction: They are encouraged to participate in activities which have an impact on welfare reform. 
Contradiction: A man is riding his bike.