石粒习惯上用大八厘、中八厘、小八厘、米粒石来表示，但这种表示方法不符合统一长度名称，其中大八厘粒径约为20mm。( )

Passage 2

Which of the following is NOT a reason of the failure to take preventive medical tests like a breast cancer screening a. Some Americans are not willing to invest in tests that might not find any problem b. Doctors are often busy and cannot afford enough time on preventive medical tests. c. Patients and doctors do not know exactly which preventive tests are really beneficial. d. There is inadequate investment in equipment and the existing tests are not effective.