My sister is good at cooking. My brother is bad at it

My sister is good at cooking. My brother is bad at it.
A. My sister is good at cooking, or my brother is bad at it.
B. My sister is good at cooking, for my brother is bad at it.
C. My sister is good at cooking, but my brother is bad at it.
D. My sister is good at cooking, so my brother is bad at it.