来源于上皮组织的恶性肿瘤称（），来源于间叶组织的恶性肿瘤称为（）。
参考答案：癌；肉瘤
360000改成用“万”作单位的数是______万，把900000000改成用“亿”作单位的数是______亿．
完成句子，使改写后的句子完整，并与原句意思相符，注意每空只填一个单词。
1. A computer is more useful than a VCD.
A VCD isn't ______ useful ______ a computer.
2. John left school after he finished his homework.
John ______ leave school ______ he finished his homework.
3. What does your father do?
What is your ______ ______?
4. How clever the boy is!
______ ______ clever boy he is!
5. I'm a doctor. He's a doctor, too.
______ he______ I ______ doctors.
