The two sounds heard through the stethoscope during a heartbeat are known as lub and dub. If the doctor detects an unusual lub sound, evaluate which description could explain the atypical sound?
1) The aorta extends during the systolic phase.
2) The mitral valve does not close after the systolic phase.
3) The aortic valve does not close during the diastolic phase.
4) The pulmonic valve does not close during the diastolic phase.
