单项选择题
We had to learn chemical（）at school but I can only remember H2O for water.
A.principles B.prescriptions C.formula D.formulae
单项选择题 At the restaurant, the only（）to chicken was beef.
单项选择题 After retiring, he（）his hobby of stamp collecting.
单项选择题 The company has（）some major changes in the last five years.
