题目

President Xi Jinping demanded the environmental problems _______paid special attention to. A . referred to be B . referred to being C . refer to being D . refer to be 答案：A如图甲所示，验电器A带负电，B不带电．用带有绝缘柄的金属棒把验电器A、B两金属球连接起来的瞬间（如图乙所示），金属棒中（ ）A．电流方向由A到BB．电流方向由B到AC．有电流但方向无法确定D．始终无电流