I suppose you'll believe a Professor of Astronomy knows what--"  
I guess you will trust a Professor of Astronomy.
I assume that you will not believe anyone but yourself.
A Che that survived his adventures would be a big change.
Because there is no opportunity to fish, if you want to eat some seafood you must go to a restaurant.
The Air Force academy is a good environment in which to build self control and maturity.
There is a man and a woman talking at a seminar.
Kids are playing outside in the summer.
The men are playing basketball.