Determine whether each set is open or closed or neither open nor closed.

a. {(x, y):y> 0} b. {(x, y): x = 2 and 1 y 3} c. {(x, y): x = 2 and 1 < y < 3} d. {(x, y): xy = 1 and x > 0} e. {(x, y): xy 1 and x >0}