mv<pv<0
i.e. mv is negative
either m or v is negative

pv is also negative, hence either p or v is negative.

question: v>0 or is v positive?

St 1 m<p
mv<pv<0 only if m and p are negative
(you can prove this by plugging numbers where both m and p are negative and one where only v is negative)
SUFF

St 2 m<0 hence m and p both are negative so v has to be positive
SUFF

Answer is D

Hope the solution is clear

we have three inequalities disguised here

mv<pv or (m-p)v<0
mv<0 and pv<0

from 1 m-p<0 hence in (m-p)v<0; v>0 suff

from 2 m<0 hence in mv<0; v>0 suff

hence D