在动物体内，（）除用于组织蛋白质合成外，还是合成维生素（）的前体。
参考答案：色氨酸；烟酸
下列哪项符合阳虚证特征()
A.手足厥冷
B.神情淡漠
C.面色苍白
D.小便清长
E.大便秘结
Helen is 15 years old, and Joan is 15, too. So Helen is ____ Joan. [ ]
A. as big as
B. as older as
C. as old as
D. so old as
