Look at the four squares,A ,B, C, and D, which indicate where the following sentence could

be added to the passage. Where would the sentence best fit？

Astronomers already knew that Mars had some kind of atmosphere because of the occasional presence of bright features that looked like clouds.

The presence or absence of water has a direct bearing on the possibility of life on other planets. A In the nineteenth century, it was commonly accepted that life, perhaps even intelligent life, was widespread in the solar system, and Mars was an obvious target in the search for life.B New photographic technology offered a way for astronomers to learn more about the red planet. In 1888, Italian astronomer Giovanni Schiaparelli produced images that showed a network of long, thin, dark lines crossing the surface of Mars.C He called these features canali in Italian, which became "canals" or "channels" in English. The strange appearance of the canals suggested to some scientists that they had been formed artificially rather than naturally.D The mystery deepened when Schiaparelli observed that many of the canals in the photographs were actually double.

A．Square Ａ.

B．Square Ｂ.

C．Square Ｃ.

D．Square Ｄ.