Questions about Stacking and Trunking

Hello, guys, recently I have learn something about stacking and trunking, and I felt confused about the following question.

1. There are three switches, two of them are belongs to one stack unit, one is unstacked. VLAN1 on stack switch 1, VLAN2 on switch 2, and VLAN3 on switch 3. Is there is a need to assign trunk port between the two stacked switches to allow communication between VALN1 and VALN2?

Someone give an answer "no". Because stack switch can be regarded as one single switch. But the trunk port is needed between the stack switches and unstacked switch.

1. Can I trunk two ports on two different switches in one stackwise unit?

Someone give an answer "yes".

What's the hell? In answer 1, a trunk port is no need between the same stack unit, but in answer 2, it's needed. Why?

Thanks for any explanation.