哪些持有Medicare 保险的人每年可以有一次免费肺癌CT检查？

官方网页：

 covers lung cancer screenings with low dose computed tomography (also known as "CT scans") if you meet all these conditions:

• You’re between 50-77. 【年龄在50-75岁（Medicare 不是65岁才能开始吗？不懂）】
• You don’t have signs or symptoms of lung cancer (you're asymptomatic). 【无肺癌症状（如果有症状就不免费了？性质由筛查变为诊断了？）】
• You’re either a current smoker or you quit smoking within the last 15 years. 【现在吸烟或者在过去15年曾有吸烟史】
• You have a tobacco smoking history of at least 20 “pack years” (an average of one pack (20 cigarettes) per day for 20 years). 【吸烟史是指每天最少一包（20根）烟吸了至少二十年】
• You get an order from your health care provider. 【医生让你检查】