下列管材中且有轻质量特点的是（）。A.钢管 B.硅铁管 C.硬聚氯乙烯塑料管

It often seems that people have a hard time in speaking a seemingly familiar name. Did you ever have someone's name on the tip of your tongue and yet you were not able to recall it? When this happened，what did you do? Next time this happens again，what should you do?
You should not try to recall it. Instead, just do something else for a couple of minutes and then the name may come into your head. Why? The name is just there, since you have met this person and learned his name. It, waiting there, only has to be dug out. The initial(最初的) effort to recall prepares the mind for operation, but it is the subconscious (下意识的) activities that go to work to dig up a dim（模糊的）memory. Forcing yourself to recall almost never helps because it doesn't loosen your memory; it only tightens it.
That’s why students find the preparatory method greatly helpful in examinations. They read over the questions before trying to answer any of them. Then they answer first the ones of which they are most confident. At the same time, deeper mental activities in the subconscious mind are taking place; work is being done on the more difficult questions. By the time the easier questions are answered, answers to the more difficult ones will usually begin to come into consciousness. It is often just a question of waiting for recall to come to the memory.
You see, forcing ourselves to think hard to recall something usually doesn’t help. Chances are that the harder we think, the more difficulty we face in thinking of what we want to. Offering our mind time to work is what we are expected to do.

Problem	People 小题1:______ to recall what they are sure they know.
Solution	They are 小题2:______ not to try to recall it immediately. They can do something else for a while 小题3:_____ of thinking hard about it.
小题4:______	It takes time for the subconscious activities to go to work to dig up a dim memory, in which case forcing oneself to recall can make the memory 小题5:_____.
Example	Students find the preparatory method of great 小题6:______ in examinations. They, having read over the questions, first answer easy ones. 小题7:_____, the subconscious activities are 小题8:_____ to deal with harder ones.
小题9:______	People should offer their mind time to work so that a dim memory can be 小题10:_____ up.