数列{a_n}中，a_n+1=a_n+2﹣a_n，a₁=2，a₂=5，则a₅为____ 

单细胞生物虽然个体微小，一般用肉眼不容易观察到，但是能独立完成____、____、____等各种生命活动．

永远的黄桷树

    常常思念大西北的白杨树，它们高大、伟岸、正直，昂首云天，不畏风寒，在严酷的环境中张扬①着坚忍不拔的性格。

    然而，白杨树只有半年的青春，那满树绿意栅栅 来迟，五月才能抽芽，十月份便被秋风染黄，还没等 冬季的时轮碾过，已卸下一身金甲，只剩下光秃秃的 枝桠，透出苍凉的意味。

    在我看来，生长在重庆的黄桷树可谓名副其实的常绿树。它枝繁叶茂，带给炎热季节的山城一片浓阴，一份凉意。即使阴雨霏霏的冬天，满树的绿也不会零落，仍是一副傲寒凌霜的姿态，仿佛一个永不疲倦的斗士，从没有卸下盔甲的日子。据说黄桷树也是年年长出芽叶，悄悄换下旧装．但在不经意之间就完成了，从来不事张扬②。

    重庆多山，地下多石，许多名花奇树似乎与此无缘，只有貌不出众的黄桷树对山城情有独钟，长势喜人。因为它拥有绵长柔韧的根须，能够从岩层、石缝里吸收养料和水分，这是它的生命力旺盛的根本原因；而且它的叶片大而密，阳光对它格外慷慨，这也是它常绿的奥秘。

    黄桷树不仅永远绿意盎然，而且具有极大的包容性。它和桐树、棕桐、玉兰树、皂荚树和谐相处，一起生长，从不因自己家族的强盛而挤兑别人，也从不在众树的簇拥下陶然欲醉。它平凡普通得犹如山城的老百姓，而它的强悍和宽容正是重庆人性格的象征。

    黄桷树以它默默无闻的奉献和吃苦耐劳的精神赢得了重庆市“市树”的美誉。从它身上，我感悟到人生的艰辛和凝重，生命的蓬勃和葱笼，也看到重庆直辖市的未来和希望。如果让我选择最喜爱的树，我会毫不犹豫地首选黄桷树。

University Room Regulations

Approved and Prohibited Items

     The following items are approved for use in residential (住宿的) rooms: electric blankets, hair dryers, personal computers, radios, televisions and DVD players. Items that are not allowed in student rooms include: candles, ceiling fans, fireworks, waterbeds, sun lamps and wireless routers. Please note that any prohibited items will be taken away by the Office of Residence Life.

Access to Residential Rooms

     Students are provided with a combination (组合密码) for their room door locks upon check-in. Do not share your room door lock combination with anyone. The Office of Residence Life may change the door lock combination at any time at the expense of the resident if it is found that the student has shared the combination with others. The fee is $25 to change a room combination.

Cooking Policy

     Students living in buildings that have kitchens are only permitted to cook in the kitchen. Students must clean up after cooking. This is not the responsibility of housekeeping staff. Kitchens that are not kept clean may be closed for use. With the exception of using a small microwave oven (微波炉) to heat food, students are not permitted to cook in their rooms.

Pet Policy

    No pets except fish are permitted in student rooms. Students who are found with pets, whether visiting or owned by the student, are subject to an initial fine of $100 and a continuing fine of $50 a day per pet. Students receive written notice when the fine goes into effect. If, one week from the date of written notice, the pet is not removed, the student is referred to the Student Court.

Quiet Hours

     Residential buildings must maintain an atmosphere that supports the academic mission of the University. Minimum quiet hours in all campus residences are 11:00 pm to 8:00 am Sunday through Thursday. Quiet hours on Friday and Saturday nights are 1:00 am to 8:00 am. Students who violate quiet hours are subject to a fine of $25.