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.