His son is now. Today it’s his birthday.A. four; four B. fourth; four C. four; fourth D.

问题补充：

His son is now. Today it’s his birthday.

A. four; four

B. fourth; four

C. four; fourth

D. fourth; fourth

答案：

A. four; four

B. fourth; four

(答案→)C. four; fourth

D. fourth; fourth

解析：句意：他的儿子现在四岁了。今天是他的第四个生日。结合语境可知前文用基数词作表语，下文用序数词作定语，故选C。