Read the sentences.
As a child, Thomas Edison asked an endless number of questions. His teachers found that he did not answer the questions they asked.
Which shows the correct coordinating conjunction for combining the sentences?
a As a child, Thomas Edison asked an endless number of questions, but his teachers found that he did not answer the questions they asked.
b As a child, Thomas Edison asked an endless number of questions, or his teachers found that he did not answer the questions they asked.
c As a child, Thomas Edison asked an endless number of questions, and his teachers found that he did not answer the questions they asked.
d As a child, Thomas Edison asked an endless number of questions, so his teachers found that he did not answer the questions they asked.