My mother is very busy with her work at the office. She still takes good care of us.  

A Because my mother is very busy with her work at the office, she takes good care of  us.

B In spite of being very busy with her work at the office, my mother takes good care of us.

C My mother is too busy with her work at the office to take good care of us.

D My mother is so busy with her work at the office that she cannot take good care of us.