Which sentence has the correct subject-verb agreement? in 1977, in the midwest, there were millions of dollars of destruction from a tornado that lasted seven hours. in 1977, in the midwest, there was millions of dollars of destruction from a tornado that lasted seven hours.

In 1977, in the Midwest, there was millions of dollars of destruction from a tornado that lasted seven hours.

Since the subject here is the Midwest which is singular the linking verb should agree with the subject as singular thus, was.

Further example,
The sentence that includes an error in the subject-verb agreement is:

A. Either June or her children are going to the movie tonight. 

This sentence should read:
Neither June nor her children are going to the movie tonight. 
"Nor" and "neither" go together and they are the negative form of "or" and "either". "Or and "either" are the positive form of "nor" and "neither". 
A good example of using "or" and "either" is the following sentence:You can either run or cycle to the shops.