【题目】—How long have you been studying at this school?
—I have been studying here ________.
A.since I was thirteen years old
B.when I was thirteen
C.at the age of thirteen
D.after I was thirteen

【答案】A
【解析】句意：—你在这所学校学习多长时间了？—从13岁开始我就一直在这学习。根据How long可知，回答应该是一段时间，只有A项表示一段时间，故选A。