根据短文内容，从短文后的选项中选出能填入空白处的最佳选项。选项中有两项为多余选项。
As you grow rapidly through your teenage years, you will experience a lot of changes. The changes may seem difficult. 小题1: Don’t panic! You will deal successfully with them! You are a young adult now!
With more responsibility, you will find more freedom to make your own choices. This is a time to be well informed about making choices. In this way you can make healthy balanced decisions. 小题2: You may already know your career path or you may have no idea at all what you want to do. Both situations are fine! Work hard and the right opportunity will present itself to you.
Young adulthood means greater freedom and more choices. 小题3: But try not to shut your family out of your life. You school learn to think of others even though you are old enough to look after yourself.
It is also perfectly natural at this time for you to spend more time with your friends than your family 小题4: A true friend will stand by you no matter what happens.
This period is a part of the life cycle. These are some people who will be with you throughout life’s journey. There will be some people with whom you part and go separate way. Leaving school can be hard. The reality is that you may not even see all of your classmates again.
You are a young adult. It is your life. No one can live it for you. 小题5:So making the right choices will be important to you. Life is for living. Enjoy your life wisely!
A．Choose your friends wisely.
B．They will help shape the future.
C．They may seem to happen quickly.
D．You will probably want to be independent. E．You may appreciate what you have in your own life.
F．The choices that you make from now on will be your choices.
G．Your family has been with you since you came into this world.
可知，有用功越大，机械效率越高，当有用功远大于额外功时，机械效率几乎不变，故本题应选B。