单选题 For centuries, physicists have had good reason to believe in the principle of equivalence propounded by Galileo: it has ______ many rigorous tests that ______ its accuracy to extraordinary precision.

【正确答案】 D
【答案解析】The physicists have had good reason to believe in the principle because it has survived rigorous or strict tests. These tests have proved that the principle is accurate. Note how the second clause supports the first, explaining why the physicists have had' reason to be confident in the principle.