This ine is tricky.. it depends on the context of the rest of the paragraph but....
MacArthur's forces _____ became isolated in the Philippines.
BECAME ... ISOLATED are both in the past tense.. I don't understand why people would use "now" for a past tense sentance. Since Mac Arthor is a historical figure the sentance is past tense, and it is a progression of events thus, "then" must be used.
I agree with with J-P.
this is fun
People obviously can't read!