The correct answer is D) The development of advanced mathematical ideas, including the Pythagorean theorem.
The statement that describes a major achievement of the classical Greek civilization is "The development of advanced mathematical ideas, including the Pythagorean theorem.
The Greeks were great philosophers and mathematicians. That was the case of Pythagoras. Greeks mathematics were based in Geometry. Thales was a great Greek mathematician, as well as Pythagoras, who developed the Pythagorean theorem. Hippocrates of Chios was another famous Greek mathematician. Let's not forget Democritus, who also developed some theories on Geometry.
