Answer: $D$
$P$(it will rain today either today or tomorrow) = $P$(it will rain today) $+ P$(it will rain tomorrow) $- P$(it will rain today and tomorrow)
So, $0.7 = 0.5 + 0.6 - P$(it will rain today and tomorrow)
$\Rightarrow P$ (it will rain today and tomorrow) =$0.4$