胆固醇合成的限速酶是（）。
A.HMG-CoA合酶
B.HMG-CoA裂解酶
C.HMG-CoA还原酶
D.MVA激酶
E.鲨烯还原酶
参考答案：C
As the years passed, many occasions-birthdays, awards, graduations__________ with Dad's flowers. [ ]
A. are marked
B. were marked
C. have marked
D. had marked
用久了的白炽灯内壁会变黑，这是由于[ ]
A．灯丝升华形成的
B．灯丝汽化形战的
C．灯丝先汽化后凝华形成的
D．灯丝先升华后凝华形成的
