Explanation:

When there is a sudden contraction in a horizontal pipe, several changes occur in the flow conditions. Let's discuss each option in detail:

Total energy decreases:
- The total energy of a fluid can be represented by the Bernoulli's equation, which states that the total energy at any point in a fluid flow system is constant.
- The total energy is the sum of the pressure energy (or pressure head), the kinetic energy (or velocity head), and the potential energy.
- When there is a sudden contraction in the pipe, the velocity of the fluid increases due to the conservation of mass. As a result, the kinetic energy (velocity head) increases. However, the pressure energy and potential energy may decrease.
- Therefore, the total energy decreases in a sudden contraction.

Velocity head increases:
- Velocity head represents the kinetic energy of the fluid due to its velocity.
- In a sudden contraction, the cross-sectional area of the pipe decreases, resulting in an increase in the fluid velocity according to the principle of continuity (mass conservation).
- As the fluid velocity increases, the kinetic energy (velocity head) also increases.

Pressure head decreases:
- Pressure head represents the potential energy of the fluid due to its pressure.
- In a sudden contraction, the cross-sectional area of the pipe decreases, causing the fluid velocity to increase.
- According to Bernoulli's equation, as the fluid velocity increases, the pressure decreases.
- Therefore, the pressure head decreases in a sudden contraction.

Summary:
- In a sudden contraction in a horizontal pipe, the total energy decreases due to changes in the velocity head, pressure head, and potential energy.
- The velocity head increases because the fluid velocity increases.
- The pressure head decreases because the fluid pressure decreases.
- Therefore, all of the given options (a), (b), and (c) are correct.