Which statement best explains the relationship between these two facts?

This question is a bit tricky, but I believe it is the answer on the bottom left. The other answers don't make quite as much sense as that one.

"Chocolate is a now sweet treat that is very popular in the United States."

It implies that chocolate wasn't always a sweet treat in the first section of the question, but if you pay close attention; it says that it "always hasn't been" a sweet treat, that use of word choice would mean it is now a sweet treat.

That's why I'd choose the one on the bottom left.

a. because the u.s. was the leading with the most technology, economy, etc. also was teamed with other allies witch boosted the economy and materials to improve technology and use it.