What different ideas did scientists in the twentieth century have about the effect of adding carbon dioxide to the atmosphere?

In the 19th century, scientists realized that gases in the atmosphere cause a "greenhouse effect" which affects the planet's temperature. These scientists were interested chiefly in the possibility that a lower level of carbon dioxide gas might explain the ice ages of the distant past.

Explanation:

the answer is definitely option c. "sonnet xxxi best illustrates the division. in the octave, the poet observes that the moon is in love. in the sestet, he gives his reaction to the fickleness of woman's love."

mark twain, real name samuel langhorne clemens, was an american writer, humorist, entrepreneur, publisher, and lecturer. among his novels are the adventures of tom sawyer and its sequel, the adventures of huckleberry finn, the latter often called "the great american novel". wikipedia