past tense ,and

i ate apple and do homework.(已過去)

and 之後do 洗唔洗轉did?? – Yes, you need to.

Your above sentence is using simple past tense.
For simple past tense sometimes we have to clearly explain which action happened first and then the next. In this case we need to use:
- simple past tense to explain the later action
- past perfect tense to explain the earlier action

E.g. : You ate the apple and then you did your homework, and you need to clearly tell people which action happened first, then your sentence should be changed to the following way:

I had eaten (past perfect tense) an apple and did (simple past tense) homework.

However, if there is no need to be that clear about which action happened first, we should just use past tense. In this case we will use the sequence(順序) of the action to tell people which action happened first.

E.g. :

I ate an apple and did my homework. (both “ate” and “did” are simple past tense, but people can understand that you ate the apple first before you did your homework.)

如果句子係
i am doing homework and watch TV??

watching? Yes, you should use watching because you are using present continuous tense : I am doing something and doing another thing at the same time.

因為两個動作都是過去了，所以要用did。
不過此句無清楚講出此两件事發立的先後次序。如果係食完apple才去做功課，可加一個then字。另apple 及homework前要加article [a, an or the]比較完整。my homework都可以。
I ate an apple and then did my homework.

2008-10-26 15:38:37 補充：
About : Doing homework and watching TV at the same time

當然要用watching 呀!

I ate an apple and did homework.

2008-10-25 12:03:04 補充：
要用did