48. Which of the following conclusions can be drawn from the author’s use of thephrase “at last” in line 3?
(A) The Earth satellites will last forever.
(B) The atmosphere will be studied after the seas and living creatures are studied.
(C) Satellites have long sought to understand the relationship of the atmosphere,the sea, and life-forms.
(D) Earth satellites play the least important role in our understanding of a singleglobal system.