Assuming that iter is a vector<string>::iterator, indicate which, if any, of the following expressions are legal

(a) `*iter++;` is legal. The expression moves `iter` to point to the next element and returns the value of the original element.

(b) `(*iter)++` is not legal. The expression means increasing value of the element, but the value is a `string` and `string` does not have `++` operator.

(c) `*iter.empty()` is not legal. Because `iter` is an iterator and has no member named `empty`.

(d) `iter->empty()` is legal. The expression means check if the string pointed by `iter` is empty.

(e) `++*iter` is not legal. The expression means increasing value of the element, but the value is a `string` and `string` does not have `++` operator.

(f) `iter++->empty()` is legal. The expression means move `iter` to point to the next element and check if the original `string` is empty.