Mars Rovers



(1) The United States space agency known as NASA launched two robot rovers to study Mars. (2) The goal was to see if Mars ever had water. (3) It has turned out to be a successful mission!
(4) The rovers launched in the summer of 2003. (5) It took them about six months to reach Mars. (6) The rovers landed on Mars with big airbags to bounce along the surface. (7) Then, the rovers drove around Mars and tested the soil. (8) These tests have shown that Mars probably once had water. (9) NASA named the two rovers Spirit and Opportunity. (10) The rovers also sent back many pictures.
(11) These rovers were meant to work for 90 days on Mars. (12) Amazingly, Spirit lasted for six years, but stopped working in 2010. (13) Opportunity continued to work more than eight years after arriving!
(14) Another robot rover named Curiosity landed on Mars in the summer of 2012. (15) This rover is bigger than Spirit or Opportunity, weighs about one ton, and is the size of a car! (16) Curiosity's mission is to see if life could have existed on Mars. (17) This rover will use lasers and other gear to test the soil.
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Due to their endurance, these two small rovers have been worth their big price tag.


The above sentence is the author's opinion. Where could this sentence be placed in the passage to support this opinion best?
A.
after sentence 13
B.
after sentence 16
C.
after sentence 2
D.
after sentence 4