问题
单项选择题 A1/A2型题
哪个时期服用四环素类药物可致恒牙发生四环素牙()
A.胚胎4个月
B.胚胎7个月
C.出生以前
D.出生至7岁以前
E.8岁以后
答案
参考答案:D
哪个时期服用四环素类药物可致恒牙发生四环素牙()
A.胚胎4个月
B.胚胎7个月
C.出生以前
D.出生至7岁以前
E.8岁以后
参考答案:D
阅读短文,根据所读内容在短文后图表中的空格里填入一个恰当的单词 Trees should be pruned(修剪)when it is necessary. A good gardener will cut away the overgrown and unwanted branches(树枝). They can make the trees more beautiful and healthier. But sometimes we’d better leave the trees to grow in their own way. Because the inexperienced gardeners will damage(毁坏) the trees. First, pruning may be done to make sure that trees in good shape or size. Maybe people want to get a tree of the right height and at the same time to help the growth of small side branches. Then people can make the tree’s appearance thick or give it a special shape. Secondly, pruning may be done to make the tree healthier. You may cut out diseased or dead branches. The health of a tree may be encouraged by removing branches that are blocking up (封闭)the center and so stopping the free movement of air. One result of pruning is that an open wound is left on the tree and this provides an easy chance for disease, but the wound will heal(愈合). Often there is a race between the healing and the disease as to whether the tree will live or die, so that there is a period when the tree is in danger. Every gardener should try to reduce that danger of death as soon as possible. It is important to make the area, which has been pruned, smooth and clean, because healing will be slowed down by roughness(粗糙). You should allow the cut surface to dry for a few hours and then pain it with one of the special materials. Pruning is usually done in winter, because you can see the shape of the tree clearly and also it is very unlikely(未必的) that the cuts you make will bleed. If this happens, it is impossible to paint them properly(合适地).
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