题目内容：
The mining industry in the U.S. became safer after the late 1960s because
A．the U.S. Senate passed laws requiring federal mine inspections. B．the U.S. Congress passed laws requiring federal mine inspections.
C．the U.S.health and safety officials passed laws requiring federal mine inspections.
D．the U.S. mine companies passed laws requiring federal mine inspections.
参考答案：
答案解析：