阅读理解。阅读下列短文, 从给的四个选项 (a、b、c和d) 中, 选出最佳选项。
us researchers have found traces of an ancient lake on mars recently，increasing hopes of discovering evidence that billions of years ago the red planet hosted life.
the lake，which dates back some 3.4 billion years，appears to have covered as much as 80 square miles and was up to 1,50
