I don't think you understand the concept of sentence stress yet, Believer. Words, either function words or content words, do not
need to be stressed; they
may be stressed, depending on what the speaker wishes to communicate. Below, I embolden the sentence stress:
I want a banana (= it's not my sister that wants one!)
I want A banana (= don't give me three or four of them!)
I want a baNAna (= not a kumquat!)
As with individual words, if the sentence us longer, there are liable to appear secondary stresses in addition to the primary stress:
When I
go to the
ZOO, I
always seem to
want a ba
NAna. (Primary stress is bold, secondary stress is underlined).