王叔叔每小时加工x个零件，3小时加工3x个．你能再举-个生活中的事例来解释3x吗？
举例为：一支铅笔3元钱，x支铅笔多少钱；
列式为3x．
一个边长4分米的正方形是由两个完全相同的直角梯形拼成的，其中一个梯形的面积是______平方分米．
The train hasn't arrived yet. Could you tell me ______? [ ]
A. why the train is late
B. that the train can come on time
C. when will the train arrive
D. why does the train arrive late
