Which word or phrase best links the ideas in this sentence? it was a great decision to take this route to avoid the school traffic. a) unless b) chiefly c) therefore d) accordingly

A and C just don't make sense. 

Here are the definitions for chiefly and accordingly:

Chiefly- above all, mainly

accordingly- in a way that is appropriate in certain circumstances

I would go with choice "B" Chiefly. The sentence was explaining that the MAIN reason to take this certain route was to avoid school traffic. 

I hope this helps you!

Brainliest answer is always appreciated!