题目

Soon a team of 200 v_____ arrived in the area to help the wounded, homeless in the earthquake without any pay.   答案：volunteers蝶、蛾类昆虫能够分泌一种物质吸引异性前来交尾，这种物质是  （     ）A．内激素B．性外激素C．蜕皮激素D．模仿性行为