A person is moving with a velocity of `10 ms^(-1)` towards north. A car moving with a velocity of `20 ms^(-1)` towards south crosses the person. The velocity of car relative to the person is
Options:
(a) `-30 ms^(-1)`
(b) `+ 20ms^(-1)`
(c) `10 ms^(-1)`
(d) `-10 ms^(-1)`