Microwaves may be great at warming up food, but what about warming people?
Using microwaves to directly heat owners of a room would save much of the energy wasted by heating walls and furniture. And despite popular ideas about microwaves, this technique would be safe, according to Charles R. Burlier of the Microwave Research Center in Marlborough, New Hampshire. Low-power microwaves only penetrate (贯穿) the skin (low-power microwave penetration in a ham is about 0.2 inches, for example) and with no negative effects.
To test this idea, Buffler subjected himself to microwaves in a special room using a standard 500-watt, 2459 MHz magnetron (磁控管). He found that a person will start to feel warmth at about 20 kilowatts per square centimeter (mw. / sq. cm. ) ; a satisfactory feeling of warmth occurs between 35 and 50 mw. / sq. cm. By comparison, a person standing in noonday summer sun feels the amount of 85 mw. / sq. cm. And a frozen meat pie in your microwave oven receives about 1000 mw. / sq. cm.
In houses of the future, each room could be provided with its own magnetron, says Buffler. When you stepped into the living room, for example, a motion detector (运动感应器)would turn on the magnetron, filling the room with low-power microwaves. In the same way that a microwave oven heats up a hamburger, but not the plate it’s on, you would feel warmth from the microwaves without changing the temperature of your coffee table. (You could, however, make your favorite easy chair even more comfortable by treating it with a radiation-absorbing chemical.)
While it might be some time before homeowners are comfortable enough with the idea to set up whole-body microwave heaters in houses, Buffler says microwaves may attract livestock(家畜) farmers. Lambs that are born outdoors in winter, for example, are frequently lost to cold. Microwaves could warm the lambs safely and quickly.
Which of the following can tell the main idea of the passage?

A．A new heating system.

B．A new microwave oven.

C．A popular technique.

D．The magnetron.

According to Paragraph 2, which of the following does not describe the characteristics of a microwave heater?

A．It directly heats people in a room.

B．It heats walls and furniture in a room.

C．It is safe.

D．It saves energy．

The test conducted by Buffler shows that when a person feels comfortable warmth, he receives about ________________.

A．20 mw. / sq. cm.	B．40 mw. / sq. cm.
C．60 mw. / sq. cm.	D．85 mw. / sq. cm.

According to Paragraph 4, which of the following fills the room with low-power microwaves?

A．The magnetron.

B．The motion detector.

C．The microwave oven.

D．The radiation-absorbing chemical.

Which of the following statements about microwave heaters would Buffler most probably agree with?

A．Microwave heaters will soon be widely used by homeowners.

B．Microwave heaters sometimes make people feel uncomfortable.

C．Perhaps microwave heaters will be first used by livestock farmers, who wish to protect their lambs in winter.

D．Microwave heaters cannot be accepted by the public because they are somewhat unsafe.