1.The Palace Museum has a large ____(collect). People can learn a lot in it.
2.When the fire happened, the firemen hurried there and carried the children to ___(safe).
3.the Chinese government has made great contributions to the ___(develop) of the world's high speed railway.
4.Last month, I took my first direct ____(fly) from Shanghai to Taiwan.
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请解释一下变形的原因。