The box was so heavy that I couldn't lift it .中为什么用couldn't 而不用can't

The box was so heavy that I couldn't lift it .中为什么用couldn't 而不用can't The box is____of apples,so it is very heavy. The box is so heavy that nobody can move it 同义句替换 The box was too heavy to carry The box is so heavy that I can't carry it.变为同义句The box is ( ) heavy ( ) him ( ) ( ). the boy is so young that he cant carry the heavy boxthe boy is not -------- --------- to carry the heavy box He is so strong that he can carry the heavy box变同义He is so strong that he can carry the heavy box .变同义句=He is strong ______ ______ ______ the heavy box. The box is too heavy for the girl to carry用so...that形式怎么写 The boy is so young to carry the heavy box.语法有没有什么错误 The boy is so strong that he can carry the heavy box.同义句 改写句子 He worked hard in order to pass the test.He worked hard( )he could pass the test.He worded so hard that he passed the test.He worked so hard ( )pass the test.The box was so heavy that she couldn't carry it.The box was( )for her( ). It was hard for her to lift the heavy box then【同义句转换】 She foud -----hard------life the heavy The box is so heavy that I can not carry it中的heavy和that之间需要加逗号吗 The box is so heavy that I can't carry it.The box is ___ heavy for me ____ _____ {改为同义句】 同义句转换The boy is so young that he can't carry this heavy box.The boy is____young_____carry this heavy box. He is so weak that he can't carry the heavy box（改为简单句）He is ___ weak ____ ___ the heavy box. the box is so heavy that i can't carry it the box is heavy I cannot carry it 为什么是so,that而不是too,that?