短文改错

     An American and a Frenchman decided to cross the sea between France and England  in the

balloon in 1784. High over the water, they discover a hole in the balloon. The hole became bigger

and bigger. The air keeps the balloon up were escaping quickly and the balloon was coming up.

The two men threw all their equipment into the water to make the balloon light. It started to rise

higher again. So it was still too close to the water. Finally, the men threw away most of his clothes

to save themselves. The crowd waiting for to greet them in England was very surprised see this when

the balloon landed on front of them.

某产品一级品比重为60%，单价为10元，二级品比重为20%，单价为5元，三级品的比重占20%，单价为4元，则该产品的平均价格为（）。

A.7.8元

B.6元

C.1元

D.9.5元