问题
选择题
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
答案
答案：C
题目分析：句意:Helen15岁了，Joan也15岁了，所以Helen和Joan一样大。根据句意可知，Helen和Joan都15岁了，所以他们两个年龄一样大。big 是指物体的体形大，不能指年龄，故Ａ不对；as…as 和…一样，表示同级比较，两个as 之间用形容词的原级。故选C。