Which of the following is/are true of tests used for screening for disease?
a. one positive screening test is not usually sufficient to diagnose a disease.
b. changes within the range of normal can be due to a disease.
c. the range of normal is not the same for all groups or populations.
d. all of these are correct.

d.All of these are correct

Explanation:one positive test is not always a guarantee that's someone can be diagnosed with a particular disease, other tests always need to be done to ensure that there is no misdiagnosis which may cause serious problems for the person who is being diagnosed.

Misdiagnosis may lead to serious issues such as prescribing the wrong medicine that may further cause complications for the patient .

A change from the range of normal can be a cause of a disease although it may not be the case at all times.

For example a spike from a normal rage of BP level of an individual patient may be the result of high blood pressure .

The range of normal also depend on age , for an old person it may be a serious cause to have even a slightest change in their BP level however it may not be much of a concern for a young health individual.