Which of the Following Clinical Symptoms Would Lead to the End

Which of the following clinical symptoms would lead to the end of a modified shuttle walk test or 6-minute walk test?

A) Patient is unable to continue per self-report.
B) Oxygen saturation is below a safe level for continued exertion.
C) Patient attains 85% of maximal predicted heart rate.
D) All of the above are valid reasons to end the test.