Grammar exercise 1 of 4 语法练习1
Use 以前、以后、以、前、后 as “以前 (yǐqián) and 以后 (yǐhòu) in Chinese grammar: before and after, past and future” explains it, through 14 items over 7 of its example sentences: fill the gap where the word was taken out, and put the words of each sentence back in order.
以前 (yǐqián) and 以后 (yǐhòu) in Chinese grammar: before and after, past and future
14 items. Each one you miss comes back later in the same sitting.