, he went to Australia to study English.
A. When a boy of 12
B. He was 12 years old
C. When he was the age of 12
D. When was 12
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(答案→)A. When a boy of 12
B. He was 12 years old
C. When he was the age of 12
D. When was 12
解析：考查省略。当主句和从句的主语一致，而从句又是主语+be动词的形式，这时从句的主语和be动词可以省略。故When a boy of 12 = When he was a boy of 12，故选A。