人体与绿色开花植物在结构层次上的主要不同是人体具有（  ）

Different countries have different customs. When you travel to another countries，please follow their customs，just as the saying goes，“             .”Very often people who travel to the United States forget to tip（付小费）.It is usual to tip porters who help carry your bags，taxi drivers and waiters. Waiters expect to get a 15% tip on the cost of your meal. Taxi drivers expect about the same amount.
In England，make sure to stand in line even if there are only two of you. It's important to respect lines there. It’s a good idea to talk about the weather. It's a favorite subject of conversation with the British.
   In Spain，it's a good idea to have a light meal in the afternoon if someone invites you for dinner. People have dinner very late，and restaurants do not generally open until after 9 pm.
   In Arab countries，men kiss one another on the cheek（脸颊）. Your host may welcome you with a kiss on both cheeks. It is polite for you to do the same.
   In Japan，people usually give personal or business cards to each other when they meet for the first time. When a person gives you a card，don't put it into your pocket right away. The person expects you to read it.Don't forget to be careful of your body language to express something In conversation. A kind of body language that is acceptable in one culture may be impolite in another.

北魏在拓跋珪统治时期,曾稳步推行“离散诸部,分土定居”的政策,该政策（    ）

如图所示，不计重力的杠杆OB可绕O点转动，重为6 N的重物P悬挂在杠杆的中点A处，拉力F₁与杠杆成30°角，杠杆在水平位置保持平衡，请在图中画出拉力F₁的力臂.