第一句肯定是错的.因为时态就不对,主语he是第三人称单数,如果该句用一般现在时的话,动词worry要变成worries,表单数,如果是用过去时的话,那就要变成worried,不能简单用worry.
他经常担心他儿子的学习,正确表述是：
He often worries about his son's studies.但这个很少用.worry about担心－－－,表示动作,很少用
He is often worried about his son's studies. be worried about固定短语,担心－－－表状态,多用