We find that bright children are rarely held back by mixed-ability teaching. On the contrary, both their knowledge and experience are enriched．We feel that there are many disadvantages in streaming pupils．It does not take into account the fact that children develop at different rates．It can have a bad effect on both the bright and the not-SO·bright child．After all，it can be quite discouraging to be at the bottom of the top grade!
By "held back" (1ine 1)the author means
A made to remain in the same class
B forced to study in the lower class
C drawn to their studies
D prevented from advancing
本题考的是对词组hold back的理解。根据上下文，它的意思是"阻挡，阻碍"，选项D是正确答案。当然hold back还可以表示(1)"犹豫"，如I have noticed that you do not hold back in our discussion．(我发觉你在讨论时并不犹豫。)(2)"控制"，如The dam was not strong enough to hold back the flood waters．(大坝不够坚固，挡不住洪水。)(3)"保留，不公布"，如I think he's holding something back：He knows more than he admits．(我认为他还隐瞒了一些事情，他知道的比他承认的多。)对照上下文，选项A、B、C都不能表达hold back的意义。