质量m=3kg的物体，在水平拉力F=6N的拉力作用下，在光滑的水平面上从静止开始运动，运动时间t=3s，求：

下列物品不需密封保存的是（   ）

⑴Where are you?____                                                         A. I'm talking to my friend.

⑵Excuse me. Where is the supermarket, please?____        B. I'm behind the tree.

⑶Thank you.____                                                                C. Turn left.

⑷Where is the train?  ____                                                  D. It's at the station.

⑸What are you doing?____                                                E. You are welcome.