Complete the sentences with the correct coordinating conjunction from the box. yet so or and

a. Teresa is an excellent employee ………………… she always has time to help others.
b. I know you were late for a good reason, …………..….I am going to give you some extra time to finish the exam.
c. Many people have complained about the poor state of extracurricular activities, ……………. no one has volunteered to help improve them.
d. I’m not sure why he acted like that. He may have been upset with us, ………………. maybe he was just tired.