1,does he have to practice speaking english every day.为什么speak要加ing?2,我不得不在六点以前到家i have to get home by 6 o'clock"以前”为什么没有before这个单词?为什么用by不用at?3,we had fun riding our bikes to the beach today为什么rid要加Ing?

practice doing sth 固定搭配
如果用了by就不用before，用before就不用by at+具体时间是指具体某一时间点，而by+具体时间的意思是到了某一时间，有一段延缓的时间，而不是就是那个时间点
have fun doing sth 也是固定搭配
希望对你有帮助

1.practice 后必须跟动名词作宾语.
2.by 在……之前.用at来表示在某一时刻,at 4∶30在4点30分;
by a time＝at that time or before／not later than that time
在那一时刻或在那一日期或不迟于那一日期
这种表示方法常暗指在那一时刻之前
The train starts at 6∶10,so you had better be at the station by 6∶10.
火车6点10分发车,所以你最好在6点10分之前到达火车站.
3.have fun doing sth.:做某事很开心 = have a good time doing sth.= enjoy
doing sth.