tenses used after "so that"

[annoussa]

hello everybody,
I really need help for my exams correction. (urgent)

Consider the sentence:
The policeman stopped tha traffic so that the blind man [crosses/ can cross/ crossed/ would cross/ could cross] the street.


What options should be left what others should be eliminated?
Does the use of the past tense "stopped", automatically implies the use of the past for "cross"?
Is it necessary to use a modal at all?



thanks in advance.

[Susan]

The correct answer is "could cross".

[annoussa]

Thx for ur answer
Any justification?