(2013·威海两校模拟)________ the earth to be flat, many feared that Columbus would fall off the edge of the earth.

A．Having believed

B．Believing

C．Believed

D．To believe

将钢锯条的下端固定在台钳上，分别用不同大小的力将锯条上端拨动一下，使它振动，如图甲、乙所示，该实验可以证明：响度与发声体的________有关，________越大，    ___________就越大。