Arithmetic series
等差级数
🧩 词语组成解析
🗣️ 情景例句
I have no time for extra-curricular activities.
我可没时间参加课外活动。
What time is the mail delivered on Saturday?
邮件在星期六什么时间被递送？
Yes, and we must stop people walking on this floor until it's firm. It may be necessary to put up a notice saying Keep off. Another thing, we' ll have to drill a hole in the wall for the electric wires.
是的，因此在地板牢固前，我们必须防止人们从地板上行走。可能还需要竖一个布告牌，写上“不得践踏”。还有，我们必须在墙上钻一个电线孔。