化简：2x-{-3y+[4x-（3x-y）]}
解：原式=x+2y
Grover Cleveland was the first president ________in the White House.
A．got married
B．to get married
C．has got married
D．was married
转氨酶的辅酶是（）
A.磷酸吡哆醛
B.焦磷酸硫胺素
C.生物素
D.四氢叶酸
E.泛酸
