如图所示，质量为m的物块放在倾角为θ的斜面体上，斜面体的质量为M，斜面体与物块无摩擦，地面光滑．现对斜面体施加水平恒力F，使物块相对斜面体静止，则恒力F大小应为（   ）

    Having a pet dog at home can be beneficial in many ways. It can teach you the value of responsibility, companionship, and caring for something other than yourself. Owning a pet dog is not just a temporary thing____You should care for your pet dog properly so you do not neglect it and help your parents train the pet dog so it is well behaved. You should also make sure you deal with any issues your pet dog is having responsibly so you do not harm your pet dog in any way.

    ____You should start by providing the necessities for your pet dog, including food and fresh water. Your parents may already have a feeding schedule set up, with set times in the day for feeding your pet dog. You should follow this feeding schedule and ask your parents if you can help it with giving your pet dog food and water on a daily basis.

    Clean up after the pet dog. You can also be a good pet owner by making sure you clean up after your dog. This means picking up any food that falls out of its food bowl and wiping up any water around its water dish so its feeding area is clean.____

    Take your pet dog for daily walks.____ You should create a walking schedule with your parents and assist your parents in walking your pet dog. You may put the collar or harness on the dog and take a tarn holding the leash during the walk, with the supervision of a parent.

    Play with your pet dog. You should spend at least ten to fifteen minutes a day playing with your pet dog so that it feels loved and acknowledged by you____

A. Give food and water to the pet dog.

B. Train your pet dog with simple orders.

C. It is a permanent responsibility that you must care for on a daily basis.

D. Never ever try playing jokes on your pet dog, because it will get hurt easily.

E. You should also use encouraging words and reward it with a treat if it behaves well when playing.

F. You can also pick up any pet toys and put them in one area so that they are not scattered all over house.

G. M you have a pet dog that is medium to large in size, you will need to walk it on a daily basis.

该生态系统中初级消费者所属营养级是(     )

夏天，被蚊子叮咬之处常会出现肿胀、瘙痒等症状，这是人体对蚊子毒素其主要成分为二 甲基亚硝胺(CH₃)₂N₂O的过敏引起的。

(1)二甲基亚硝胺是由____  种元素组成的；

(2)科学家实测出蚊子口器刺入皮肤的平均刺入力为1．65×I0^-6牛，这么小的力能刺穿皮肤是因为减少____ 而增大了作用效果。

阅读下面选文，完成小题。
      陈胜、吴广乃谋曰：“今亡亦死，举大计亦死；等死，死国可乎？”陈胜曰：“天下苦秦久矣。吾闻二世少子也，不当立，当立者乃公子扶苏。扶苏以数谏故，上使外将兵。今或闻无罪，二世杀之。百姓多闻其贤，未知其死也。项燕为楚将，数有功，爱士卒，楚人怜之。或以为死，或以为亡。今诚以吾众诈自称公子扶苏、项燕，为天下唱，宜多应者。”吴广以为然。乃行卜。卜者知其指意，曰：“足下事皆成，有功。然足下卜之鬼乎？”陈胜、吴广喜，念鬼，曰：“此教我先威众耳。”乃丹书帛曰“陈胜王”，置人所罾鱼腹中。卒买鱼烹食，得鱼腹中书，固以怪之矣。又间令吴广之次所旁丛祠中，夜篝火，狐鸣呼曰：“大楚兴，陈胜王”。卒皆夜惊恐。旦日，卒中往往语，皆指目陈胜。
      吴广素爱人，士卒多为用者。将尉醉，广故数言欲亡，忿恚尉，令辱之，以激怒其众。尉果笞广。尉剑挺，广起，夺而杀尉。陈胜佐之，并杀两尉。召令徒属曰：“公等遇雨，皆已失期，失期当斩。藉第令毋斩，而戍死者固十六七。且壮士不死即已，死即举大名耳，王侯将相宁有种乎！”徒属皆曰：“敬受命。”
                                                                                                                              （节选自司马迁《陈涉世家》）