在E-R图中，矩形表示______。
参考答案：实体
解析： 在E-R图中用矩形表示实体；椭圆形表示属性；菱形表示联系。
—Hi, Mr. Smith. Which department do you work in?
—I am in the Marketing Department now, but I ________ in the Sales Department before long.
A．worked
B．will work
C．have worked
D．will have worked
化学实验是科学探究的重要手段之一。下图所示的基本操作正确的是[ ]
A.
B.
C.
D.
