A, liquid carbon dioxide fire extinguishers will not damage objects because they leave any traces, and are used to put out fires such as books, files, expensive equipment and precision instruments, so A meets the meaning of the question;

B, fire hydrant is used to put out the general fire; Therefore, b does not meet the meaning of the question;

C, dry powder fire extinguishers can be used to put out general fires, and can also be used to put out fires caused by oil and gas. , so c does not meet the meaning of the question;

D, foam extinguisher can be used to put out wood, cotton and other general fires, so D does not meet the meaning of the question.

So choose a.