III: Rational Cloze (44%) Choose the best answer for each missing word or phrase in the following excerpted passages. Passage 1: Questions 21-24 Astronomers have discovered a planet three times the mass of Jupiter that travels on a long,egg-shaped path around its star. If this planet __(21)__ somehow placed into our own solar system, itwould swing from within our asteroid belt to out beyond Neptune.The planet was discovered using the radial velocity method, also known as Doppler spectroscopy.The radial velocity method is the most effective method for locating extrasolar planets__ (22)__ existing technology. It relies on the fact that a star does not remain completely __(23)__ when it isorbited by a planet. It moves in a small circle or ellipse, responding to the gravitational tug of its smallercompanion. When__ (24)__ from a distance, these slight movements affect the star's normal lightspectrum, or color signature.
【題組】21.
(A) was
(B) were
(C) has been 
(D) had been