According to the "geological time" section in the reading by backman and seeds (2010) on life in the universe, the 4.6 billion year history of earth can be represented by the calendar year. in which calendar month would the dinosaurs have appeared

December (12th month)

Explanation:

According to Wikipedia, dinosaurs existed in about 243 million years ago on earth.

Of the 4.6 billion years history of the earth, when we divide it into 12 months.

4.6billion/12 = 383.33 million years

That means each month last 383.33 million years.

Therefore, the 243 million years ago when dinosaurs existed still lies within the 12th month ( the 12th is between 383.33million years ago till date)

Hence, the time of dinosaurs will be in December (12th month).

a and b because with the other three, they simplify to something else.