题目内容：

    Researchers have confirmed that there are several effective methods for cleaning the N95 masks worn by health professional so that they can be used more than once,the National Institutes of Health announced Wednesday.

A research already showed that the masks,designed for one-time use,can be reused in a crisis.And the Centers for Disease Control and Prevention in March authorized reuse because of shortages driven by the Covid-19 pandemic.

None of these rules or methods are intended for the cloth masks recommended or in some locations required for use by everyone in public.

Earlier research had not,of course,involved the new coronavirus.The new research determined which cleaning procedures were most effective.

N.I.H.publicized the study because it could be helpful to health care professionals in the crisis.Dr.Munster and his colleagues tested four methods of killing the virus:UV light,dry heat, vaporized hydrogen peroxide(YHP)(汽化过氧化氢）and ethyl(乙醇）alcohol.Of those methods,they did not recommend ethyl alcohol because although it killed the virus,it degraded the mask material.

Vaporized hydrogen peroxide,a method often available in large hospitals,was effective, and left the masks still functioning for at least three rounds of cleaning,as did UV light.

Dry heat,at 70C,was effective,but the masks withstood only two rounds of cleaning.Dr. Munster said that"vaporized hydrogen peroxide would be the method of choice if that's available."However,he said,a nursing home might not have that,while for dry heat,what's needed is basically an oven.

Another recent study from Canadian researchers confirmed the value of cleaning.It included masks of different brands and found that the material of the mask was still effective after 10 rounds of vaporized hydrogen peroxide cleaning.

The findings are intended to be useful for health care workers wearing N95 masks.With personal protective equipment in short supply at many overwhelmed hospitals,some front-line workers have complained that masks were rationed.

The public has been advised not to use or try to buy N95 masks because they would be preventing health care workers from having lifesaving equipment.

1.Of the different cleaning procedures of N95 masks,which one is the least effective?

A.UV light B.dry heat

C.vaporized hydrogen peroxide(VHP) D.ethyl alcohol

2.In a dictionary,the underlined word"ration”has the.following explanations.Which explanation do you think agrees with the context?

A.a fixed allowance of something that is scarce

B.the amount of something one normally has

C.to assign to someone for a particular purpose.

D.to restrict the distribution of something

3.What's the main idea of the passage?

A.The public has been advised not to use N95 masks.

B.The health care workers are in great need of N95 masks.

C.N.I.H.announced N95 masks can be reused if cleaned effectively.

D.Personal protective equipment is in short supply at many hospitals.