The correct options are as follows:
1.GRAVITY.
 Mass movement refers to the movement of surface materials such as soils, mud, rocks, etc down a slope. The force of gravity is responsible for pulling the materials down the slope. Mass movement usually occur along mountain side and hill side as a result of angle of repose of the land form involved.

2. MASS MOVEMENT ALWAYS LEADS TO LANDSLIDE.
This statement is not true, mass movement does not always result into landslides. Mass movement basically leads to bulk movement of earth surface materials from one location to another location. It can happen rapidly or gradually over a long period of time.

 3. THE ANGLE OF THEIR SLOPES IS GREATER THAN 40 DEGREE.
 The principal cause of mass movement is the slope angle of the land form concerned. If the angle is overly steep, that is, above 40 degrees, the force of gravity will pull the surface materials downward causing a mass movement.

4. SLUMP.
 Slump refers to the downward movement of large segments of earth surface, which occur when the base of a land form can no longer support the weight at the top of the land form. The sediments usually break off in one piece and water is usually one of the factors that lead to the break off.

 5. MUD FLOW.
 Mud flow refers to the type of mass movement that involves rapid, surging flow of materials that has been made liquefy by the addition of water. Mud flow usually contains large amount of clay, which makes it fluid in nature and enhances its ability to travel over long distances. Mud flow is usually made up of different materials which have different sizes.

6. EVAPORATED.
 Huge amount of water are usually evaporated from different water bodies on a daily basis as a result of heat from the sun. When the cloud become saturated with the evaporated water, the water is release back to the earth in form of rainfall. Thus, the amount of water evaporated from the earth surface and the amount of rainfall released to the earth are usually of equal amount.

7. VELOCITY.
 The velocity of a river refers to the speed with which the water body moves through its channels. Water velocity is usually highest near the surface and lowest near the bottom. The higher the velocity of a water body, the higher will be its ability to transport materials and the reverse is also true.

 8. GRADIENT.
Gradient refers to the stream grade, which is measured based on the ratio of drop in elevation per horizontal distance. It is usually measured in meter per kilometer or feet per mile. A high gradient implies a steep slope and rapid flow of water while a low gradient translate to slowly moving water.