question in the simple past

why do we say "which was the last movie you saw?" and not "which was the last movie you see?"

[Casiopea]

A. Which movie did you see last?

In sentence A. did...see represents the past tense.


B. Which was the last movie you saw?

Sentence B. means,

[The last movie you saw] was which?

1) Move 'was which' to the front:

was which [the last movie you saw?]

2) Invert the subject 'which' and the verb 'was':

which was [the last movie you saw?]

'was' is the sentence's main verb; 'the last movie you saw' is the object of the main verb.

:D