Read the following statements and find out which of these are correct using the codes placed after the statements:

(a) Herodotus declared earth as a flat disc.

(b) Main contribution in the field of historical and mathematical geography came from the Romans.

(c) Eratosthenes was the first to calculate the tilt of the earth's axis.

(d) Ptolemy accurately assumed the circumference of the earth which helped sailors reaching Asia by sailing West from Europe.