COMB in N-COUNT （美国英语用法，用于first, second等词后构成名词）表示“…年级学生” -grader combines with words such as 'first' and 'second' to form nouns which refer to a child or young person who is in a particular grade in the American education system. （美国英语用法，用于first, second等词后构成名词）表示“…年级学生”