Asubmarine started at sea level and was 400 meters below sea level in 10 minutes.
which statement correctly explains the submarines rate of movement?

Because it is BELOW sea level after 10 minutes, it straight away cannot be A) or B), because ascended means going up, so it has to be either C) or D). 

I believe the answer is C), as the answer for D) would be -40 meters per minute, but it's still 40. I'm not sure though, so it's either C) or D).