因为前面有help加了s，help sb. do sth,所以用cleanTom ofen helps his mom clean the room.
第三人称动词形式也要相对应，就算是“经常”也是一样的，除非用现在进行时或某些动词的不定式搭配。这可是最基础的时态一致的问题啊。。。。。。
最好写出你的原题来。
Tom always helps his mother clean the room.
help do sth
