The system of __ emerged in medieval Europe and was chiefly of a military nature, whereby people owed service to a lord.

By the time of Muhammad, the __ had become an important trade center since fighting was banned in the sacred space.

__ were soldiers in the Abbasid caliphate who had been young boys converted to Islam and then trained as soldiers.

In the eighth century BCE, rulers from which kingdom took over the throne of Egypt?

True or false? Gold and salt were the two most important goods traded by medieval empires in West Africa.

Match the components to its function

Which of the following structures receives oxygenated blood from the lungs via the pulmonary veins?

When the cells undergo aerobic metabolism, which one of the following occurs?

Which of the following structures has leaf like cuplets to prevent the backflow of blood?

Which valve of the heart does blood pass through after leaving the left atrium?