He can't be back yesterday.
解析：
所谓同义句转换就是将一个句子用另一种形式表达出来，而且意思不变。因此，掌握的句型越多，做题就越方便、快捷、容易。但每种练习的方式总有一定的规律可循。
1. 用具有相同意思的词或词组进行转换。如：
例：She has a good time in Wuhan.
转换：She enjoys herself in Wuhan.
例：He spends some money on books every week.
转换：He pays some money to buy books every week.
2. 借助于反义词或反义词组进行转换。如：
例：I can’t run as fast as my brother.
转换：I run more slowly than my brother.
My brother runs faster than I.
例：He is not old enough to go to school.
转换：He is too young to go to school.
3. 词语的理解和运用
这里是指：由于词性不同，但所表达的意思相同的句型变换。如：
例：We often go to school on foot.
转换：We often walk to school.
追问要变为He ( ) ( ) to come back yesterday.
追答He wasn't able to come back yesterday.
he could not come back yesterday.(他昨儿没能来。)
追问谢谢！