Which one of the following displacement-time graphs represents two moving objects $P$ and $Q$ with zero relative velocity?

$A$ thief is running away on a straight road in a jeep moving with a speed of $9 \, m/s$. $A$ policeman chases him on a motorcycle moving at a speed of $10 \, m/s$. If the instantaneous separation between the jeep and the motorcycle is $100 \, m$,how long will it take for the policeman to catch the thief?

Two trains $A$ and $B$ of length $400 \; m$ each are moving on two parallel tracks with a uniform speed of $72 \; km \; h^{-1}$ in the same direction,with $A$ ahead of $B$. The driver of $B$ decides to overtake $A$ and accelerates by $1 \; m \; s^{-2}$. If after $50 \; s$,the guard of $B$ just brushes past the driver of $A$,what was the original distance (in $m$) between them?

An express train is moving with a velocity $v_1$. Its driver finds another train moving on the same track in the same direction with velocity $v_2$. To escape a collision,the driver applies a retardation $a$ to the train. The minimum time to escape a collision will be:

Two bodies start moving from the same point along a straight line with velocities $v_1 = 6 \, m/s$ and $v_2 = 10 \, m/s$,simultaneously. After what time will their separation become $40 \, m$?

Two buses $A$ and $B$ are moving in opposite directions. If the first bus $A$ moves towards the east with a speed of $36 \ km/h$ and bus $B$ moves towards the west with a speed of $18 \ km/h$, then the bus $B$ appears to bus $A$ as: