Technological advances had helped reveal that the ocean floor was not flat, as once believed, but instead was marked by 50,000-kilometer-long, 3,000-meter-high ridges and 11-kilometer-deep trenches. How do scientists explain why, if new crust is constantly being formed from volcanic materials at the ridges, Earth's crust stays the same size?

A) Seafloor spreading is the cause of new crust being added. Old crust crumbles and forms mountains throughout the Earth's surface. Mountains keep growing.
B) Scientists hypothesize that new crust is the result of volcanic activity throughout the Earth's surface and older magma is destroyed as it subducts during earthquakes into Earth's mantle.
C) Scientists found that the youngest oceanic crust is located nearest the mid-ocean ridge and divergent boundary and the oldest crust is at subduction zones where it sinks back into the Earth.
D) Scientists found that the oldest oceanic crust is located nearest the mid-ocean ridge and forms from volcanic activity;the youngest crust is nearest the trenches and it comes from magma flowing up to Earth's surface..

Are there options for this?

    m₁v₁ + m₂v₂ = (m₁ + m₂)vmomentum is conserved.the left-hand side of the equation represents the momentum in the system before the collision.the right-hand side represents the momentum in the system after the collisionm₁ and v₁ represents the mass and the velocity of the physics blockm₂ and v₂ represents the mass and velocity of the ball of puttyv represents the final velocity of the combined mass.the question states the two masses stick together. they combined mass has its own velocity with the body mass the sum of the two objects' massestheir combined momentum is (m₁ + m₂)vto find the magitude of (m₁ + m₂)v, we need to add the vectors on the left-hand side of the equation: m₁v₁ + m₂v₂.note the diagram. i have positioned the vectors in accordance with their directions.the magnitude of the resultant can be calculated using the pythagorean theorem since this is a right triangle situation (north and west are perpendicular)|(m₁ + m₂)v| =  √[ (m₁v₁)² + (m₂v₂)² ]|(m₁ + m₂)v| =  √[ (1.5kg·8.0m/s)² + (0.40kg·20m/s)² ]|(m₁ + m₂)v| =  14.4 kg m/sfor two significant figures (assuming that 20m/s is two), this rounds to 14 kg m/s