lessen/shorten the requirment ?

intended primarily to stimulate family summer travel,the new aurfare,which allows both an adult and a child to fly for the price of one ticket,and also shortens the advance-purchase requirment for family travel to a minimum if seven days rather than fourteen.

就有一个问题：

d. also lessens the advance-purhase requirment for family travel to a seven-day minimum from

e. also shortens the advance-purhase requirment for family travel to a minimum of seven days rather than.

答案是e,但我怎么看怎么觉得d 的lessen the requirment 更好呢？