第 16 至 20 題為題組
     Astronomers have discovered the darkest alien planet known to exist in the galaxy.
     The Jupiter-sized planet, known as TrES-2b, is located in another solar system some 750 million lightyears away from Earth. Reflecting less than one percent of the sunlight   16   on it, TrES-2b is lessreflective than black acrylic paint, and is blacker than coal. The only light that comes from TrES-2b is afaint red glow,    17    the heated coils on an electric stove or a very dim light bulb. Researchers believethis results from its extremely hot atmosphere, which is as high as 1,800°F (980°C),   18    its closenessto its sun—its source of energy.
     So how does this planet manage to absorb about 99% of the light it receives from its sun?   19  researchers are not completely sure, they believe it could be because its atmosphere is composed of lightabsorbing chemicals like vaporized sodium or even some elements whose existence is not yet known.Although they may never be able to   20   exactly how the planet remains so stealthily hidden, scientistsare sure of one thing—there are many more even darker planets out there just waiting to be discovered!
【題組】16.
(A) falls
(B) falling
(C) fallen
(D) to fall