When we want to tell other people what we think, we can do it with the help of words. We can also do it in many other ways, too. Sometimes we move our heads up and down when we want to say "yes", and we shake our heads when we want to say "no " Some people can’t hear or speak. They talk with the help of gestures(手势). People from other countries often have to do it if they don’t know your language.
Here is a story. An American was once having his holiday in Italy, but he could not speak Italian. One day he went to a restaurant and sat down at a table. When the waiter came, the American opened his mouth, put his fingers in it and took them out again. In this way he wanted to say "Bring me something to eat". The waiter soon brought him a cup of tea. The American shook his head and the waiter understood that he didn’t want tea. So he took it away and brought him a glass of milk. The American shook his head again. He was very hungry now and looked sad. He was just going to leave the restaurant when another man came in. When this man saw the waiter, he put his hands on his stomach (胃). In a few minutes there was a large plate of bread and meat on the table in front of him.

Sometimes people move their heads ______ when they want to say "yes".

A．right and left

B．fast and slow

C．hard and easy

D．up and down

用火化验分析标准中，爆炸下限小于4％的可燃气体，其可燃物含量小于或等于（）为合格；爆炸下限大于或等于4％的可燃气体，其可燃物含量小于或等于（）为合格。

A、0.2％；0.5％

B、0.2％；0.2％

C、0.5％；0.5％

D、0.5％；0.2％