Expressing gratitude is an important form of good manners. Nowadays more and more people in China have found it’s high time to (1) a thankful heart for the young.Everyone likes to get praised and appreciated. Gratitude is the greatest of virtues, which lets others smile and makes the world more beautiful. You just need several minutes to write down a thank-you note, but it brings much joy to the (2) .We live in a society where we enjoy the different services of others. But (3) of them should be taken for granted.Gratitude is also a kind of (4) in life. In developing gratitude for every moment—for the simple joys and even for the (5) times—we come to truly enjoy and appreciate life. Then we are able to see the (6) that surrounds us.Try to write a thank-you letter to your parents for working hard to (7) you a happy life.Be grateful to your teachers because of their (8) with your studies and character building.Say thanks to your friends who (9) both your happiness and sorrow. We are sure it will bring them much joy and add (10) into your own life as well.

第（9）空应选择（）

A．knew

B．shared

C．realized

D．recognized

为防止氧的有害影响，操作时应严格控制（）。

A.火焰的温度

B.焊接速度

C.火焰性质