One Technique That Astronomers Are Now Using to Increase the Amount

One technique that astronomers are now using to increase the amount of detail that can be recorded with telescopes is

A) spinning huge tubs of mercury, thus producing very large parabolic surfaces at relatively low cost.
B) antireflective coatings, where the mirror is coated with a substance such as calcium fluorite to reduce the amount of reflected light.
C) increased size, with mirrors up to 10 m in diameter (far larger than at earlier times) , thereby producing greater intrinsic angular resolution.
D) adaptive optics, where the tilt and shape of mirrors in the telescope are changed many times per second to compensate for atmospheric turbulence.