Midterm review question...

if my notes are correct, the answer for A1 Q1 is...

a, b, and c

Can someone explain why d, e, and f are not an answer?

(I don't recall the explanation given in class)

Not D because although you can have any number of 1's and 0's before the mandatory 0, you can then only have 0's following that. You must be able to have 1's at the end as well in order to satisfy any string, i.e. the string can only terminate with 0's in this answer.

Not E because you can only have optional 0's before the mandatory 0 in the middle, i.e. the allowable strings could only begin with 0 with this answer.

Not F because this answer does not allow any strings that end with 1's.

Not G because this answer does not allow any strings with 1's in them.

I hope this explanation helps.