选C
解析:He works harder than ___in his class.这句话根据选项可以看出意思为:他比他们班的其他同学更努力,换句话说,他是他们班最努力地学生.
C.any other student 任何一个学生
D.other students其他学生,不含特指之意
而这里,in his class本句中是指在他们班的同学,如果要用other,应用特指,即:the other students,所以选C不选D (any other students = the other students )
另外,这句的两个同义句为:He works harder than any other students in his class.
=He works harder than the other students in his class.
=He is the hardest sthdent in his class.
(用比较级表示最高级,特殊词是:in...或者of.)