简述离体培养技术在园艺育种上的应用？

其遗传方式为

A．常染色体显性遗传

B．常染色体隐性遗传

C．X连锁显性遗传

D．X连锁隐性遗传

E．X连锁不完全显性遗传

如图，三根绳子上的拉力分别是T₁、T₂和T₃，若悬点B不动，悬点A水平向左移动时，对三根绳子上拉力的变化情况中不正确的是（　　）

A．只有T₃不变

B．T₁和T₂均变小

C．T₁和T₂均变大

D．T₁和T₂的合力不变

The person behind you constantly kicks the back of your seat．Your talkative seatmate doesn’t understand your need for sleep．And the aircraft’s bathroom is a total mess．These situations can make even a short flight unbearable．Hopefully you don’t cause these unpleasant experiences for others．Instead，you can set an example by following these common airplane courtesies．

Always recline your seat slowly．There’s nothing worse than suddenly being slammed in the knees by the seat in front of you．In addition，don’t keep your seat reclined for the entire flight．Always keep it upright position before going to the restroom（or anytime you leave your seat）．

Avoid going to the bathroom during mealtime．Wait until the meal is done and all the food trays have been collected．It’s hard for passengers to stand up to let you pass when they still have their food trays．And when using the bathroom，always clean up after your-self-the next user will be grateful!

Keep your body--and your possessions-to yourself as much as possible so as not to crowd your in-flight seatmate（s）．Share the armrest，especially on a long flight．Also，be careful not to kick or push on the seat in front of you，and don’t allow your children to do so either．

While some people enjoy chatting with other passengers during a flight，not everyone does．Some people may want to nap，read or work．If the conversation seems one—sided，take the hint．

If you are traveling with someone and want to chat，keep your voices low．If using electronic gadgets，keep the volume down．People can still hear through your headphones if the volume is too high．

When exiting the plane，if others are having trouble with their carry-on luggage，help them if you can．If you can’t help，wait patiently，and don’t push past people to get off the airplane．

On your next flight，remember that it all boils down to the golden rule．Treat others the way you want to be treated !

72．Which of the following manners we should follow while flying?

A．Always keep your seat upright during meal time．

B．Keep your belongings to yourself as much as possible．

C．Use your headphones and keep the volume down．

D．All the above．

73．Where do we most probably read this passage?

A．a text book                                               B．a newspaper

C．a magazine                                                 D．a science book

74．Which of the following word has the closest meaning with the word courtesies?

A．golden rules            B．manners                  C．experiences             D．passengers

75．What is the best title of this passage?

A．Manners in the sky．

B．Bad manners in the sky．

C．Behave yourself in the sky．

D．Treat others the way you want to be treated．

什么是进汽机构的节流损失？它与哪些因素有关？如何减少该项损失？