Two particles A and B, move with constant velocities

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Two particles A and B, move with constant velocities v^{^→}₁ and v^{^→}₂. At the initial moment their position vectors are r^{^→}₁ and r^{^→}₂ respectively. The condition for particles A and B for their collision is :

1. r^{^→}₁ . v^{^→}₁ = r^{^→}₂ . v^{^→}₂
2. r^{^→}₁ × v^{^→}₁ = r^{^→}₂ × v^{^→}₂
3. r^{^→}₁ - r^{^→}₂ = v^{^→}₁ - v^{^→}₂
4. r₁^{^→} - r₂^{^→} = v₂^{^→} - v₁^{^→}
  | r₁^{^→} - r₂^{^→} | | v₂^{^→} - v₁^{^→} |

Correct Option: D

For collision V_B/A^{^→} should be along
B ≻ A(r_B/A^{^→})

So ,	V₂^{^→} - V₁^{^→}	=	r₁^{^→} - r₂^{^→}
	\| V₂ - V₁ \|		\| r₁ - r₂ \|