单选题 Why should anti-virus software be updated at least once a week?

A、 Because the newly published anti-virus software is more expensive.
B、 Because the previous(先前的) anti-virus software cannot work any longer.
C、 Because the inventors of viruses have suggested this idea.
D、 Because computer viruses are always developing.

【正确答案】 D

【答案解析】[解析] 事实细节题。从文章第二段第一句话，Anti-virus software is a must，and it should be updated at least once a week to recognize newly viruses．我们可以看出，新的计算机病毒总是在不断地出现、不断地升级换代。以前的防毒软件可能不行了。所以正确的答案为D。