A

Step 1: Understand what cathode rays are. Cathode rays are streams of electrons that are emitted by the cathode in a vacuum tube.
Step 2: When these high-speed electrons collide with a metal target, significant energy is released due to the sudden deceleration of the electrons.
Step 3: According to the principles of electrodynamics, when charged particles such as electrons are decelerated, they emit electromagnetic radiation. This high-energy radiation is what we commonly refer to as X-rays.
Step 4: The high melting point of the target allows it to withstand the thermal energy produced during these fast electron impacts without vaporizing, ensuring effective X-ray production.
Conclusion: Therefore, when cathode rays strike a high melting point metal target with very high velocity, they produce X-rays.
Thus, the correct answer is option A.