In Arabic if the sentence start with a noun called مبتداء and this noun followed by another noun call الخبر and this two nouns suppose to match each other (Single ,plural, male/female)
الطالب المجتهد
الطالبة المجتهدة
الطالبان المجتهدن
الطلاب المجتهدون
الطالبات المجتهدات
But this rule doesn't work when the sentence start with a verb because the verb followed by a noun called فاعل
اجتهد الطالب
اجتهد الطلاب