题目

________ the danger of traveling on the lonely island, they would not be trapped now. A . Have they been informed of B . Were they informed of C . Should they be informed of D . Had they been informed of 答案：D氢气球重10N，空气对其浮力为16N，由于受水平风力的作用，氢气球的绳子和地面成θ=60°，如右图所示，由此可知，绳子的拉力为______N，水平风力是______N．