如何区分 did,didn't ,do ,does ,doesn't
how used
did,didn't ,do ,does ,doesn't ??????

Question

如何区分 did,didn't ,do ,does ,doesn't
how used 
 did,didn't ,do ,does ,doesn't ??????

Answer

Present tense: do / does(he/she/it)

Past tense: did

Negatives: don't / doesn't, didn't

Answer

Do (present)  I do study Chinese.
Didn't/did (Past) I didn't eat it.  I did eat it.
Does/doesn't (He/she with present) He does eat apples.  He doesn't eat apples.