Cathode rays haveA only mass. B only charge. C neither mass nor charge. D both mass and charge.

Answer Analysis

Cathode rays are streams of electrons emitted from the cathode in a vacuum tube. The characteristics of cathode rays can be analyzed as follows:

1. Nature of Cathode Rays: Cathode rays are primarily composed of electrons, which are subatomic particles that possess both mass and charge.

2. Mass of Cathode Rays: Electrons have a small mass (approximately $9.11 \times 10^{-31}$ kg).

3. Charge of Cathode Rays: Electrons carry a negative charge of approximately $-1.6 \times 10^{-19}$ coulombs.

Conclusion

Given the characteristics of cathode rays, the correct answer is:

D: both mass and charge.

This means that cathode rays consist of particles (electrons) that have both mass and negative electric charge.