There is little chance that we will succeed in changing the law. ______, it is important that we should have a try.

A．Therefore

B．Otherwise

C．However

D．Thus

让足球和铅球都静止在地面上，足球轻轻一踢就能运动起来，但要使铅球运动起来却不那么容易，请你分析以上情景，提出一个你认为应该探究的问题：___________ _______________________________________________________。