He always devotes his time to helping children with their studies rather than_ games on computer.

B
因为playing是和helping并列的可不是有rather than do这个词组吗？rather than 有连词和介词两种用法，你说的那种是连词用法，此句中是介词用法。rather thanconj.（连接词）And not:而不是…，而非…：“Gibson guitars—with their carved tops and necks that are fitted and glued to the body, rather than bolted on—are expensive to make”(Joshua Rosenbaum)“制造吉伯逊吉他非常昂贵——精雕的顶端和颈部被安装且黏到吉他主体，而不是被锁上”(乔舒亚·罗森鲍姆)prep.（介词）Instead of:而非…，替代…：“diseases in which the immune system plays the villain rather than the protector”(Sandra Blakeslee)“免疫系统在疾病中扮演的是坏蛋的角色，而非保护者”(桑德拉·布莱克斯利)怎么判断 rather than 是用作连词还是介词呢？