Answer: B. Dustproof and waterproof.
Answer analysis: When discussing the IPXX rating of the display screen, we must first understand the meaning of the IP rating. The IP rating consists of two numbers. The first number indicates the level of dustproof and foreign body intrusion prevention of the appliance, and the second number indicates the degree of airtightness of the appliance against moisture and water intrusion. Both numbers are defined according to the standards drafted by the International Electrotechnical Commission (IEC).
Now, let's analyze the options one by one:
A. Dustproof and moistureproof
- The "moistureproof" in this option does not accurately correspond to the meaning of the second number in the IP rating. The second number in the IP rating is used to indicate waterproof capability, not moisture-proof.
B. Dustproof and waterproof
- This option accurately describes the meaning of the two numbers in the IP rating. The first number represents the dustproof level, and the second number represents the waterproof level.
C. Waterproof and dustproof
- This option reverses the meaning of the two numbers and does not meet the definition of the IP rating.
D. Moisture-proof and dust-proof
- Similar to option A, "moisture-proof" is not the meaning of the second number in the IP rating.
In summary, when the protection level of the display is expressed as IPXX, the first X represents the dust-proof level and the second X represents the waterproof level.
Therefore, the correct answer is B. Dust-proof and waterproof.