造血干细胞的免疫标记是A．CDl4 B．CDl9 C．CD34 D．CD38 E．C
题型：单项选择题
问题：
造血干细胞的免疫标记是
A．CDl4
B．CDl9
C．CD34
D．CD38
E．CD4l
题型：单项选择题
| 阅读短文，从方框中选择合适的词语，并用其适当形式补全短文。 | |
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| Over the past ten years, great changes (1)________ in our hometown. (2)________, the houses in our hometown were very old  , (3)________ now most of the people have moved into tall buildings. The water in the river (4)________ very dirty, but now the river is very clean, and we can swim in it. People he  re used to walk or ride bikes, but now they can take buses or drive their own cars (5)________. |
ce, in the past, go to work, used to be