prepostion

[sherly]

Hai iam sherly,

i just want to clarify a doubt about the prepostion before the qustion is can i use a past form of the verb next to the prepostion before?
as in this sentence

i wrote a letter before i left the classroom
is this sentence correct?
or

i wrote a letter before i leave the calss room

is this sentence wrong if so give me the reason

hope for your reply as soon as possible

[hector51]

hi!

i wrote a letter before i leave the calss room

This sentence is wrong,because both of the two actions were taken in the past,so you have to use the simple past tense in both 2 clauses!

the preposition "before" is used to show which action happened first.just use the simple past in both 2 clauses

[sherly]

sory iam not clarified with your explanation and even i feel it a mistake that the both actions was taken is a wrong sentence can you explain me detail that about the use of prepostion before and untill because i was given instuction by a teacher that i should not use a past form of a verb next to certain prepositions

so please give me a detailed explnation