Instructions: Select the answer that logically joins each pair of simple sentences with coordinating conjunctions, subordination conjunctions, or conjunctive adverbs and is punctuated correctly.

I couldn't bring the clients both to and from the conference. Betty offered to drive one way.

a. Betty offered to drive one way, because I couldn't bring the clients both to and from the conference.
b. Because I couldn't bring the clients both to and from the conference, Betty offered to drive one way.
c. Betty offered to drive one way so I couldn't bring the clients both to and from the conference.
d. I couldn't bring the clients both to and from the conference, therefore Betty offered to drive one way.