Starting with the （）that there is life on the planet Mars, the scientist went on to develop his argument.

A．Those who don't emphasize bookish excellence in their pursuit of happiness.
B．Those who are aware of difficulties in life but know how to avoid unhappiness.
C．Those who measure happiness by an absence of problems but seldom suffer from N. B. D. 's.
D．Those who are able to secure happiness though having to struggle against trying circumstances.

A．difficulties are but part of everyone's life
B．depression and unhappiness are unavoidable in life
C．everybody should learn to avoid trying circumstances
D．good feelings can contribute to eventual academic excellence