Answer: Where would the blood come from if there were a blockage just posterior to the middle cerebral artery on the left? If blood could not get to the middle cerebral artery through the posterior circulation, the blood would flow around the circle of Willis to reach that artery from an anterior vessel.
Explanation:
The First 20 Elements and The Difference Between Elements, Compounds and Mixtures. Standard. 1 – H – Hydrogen – Odorless, Colorless and Flammable Gas. 2 – He – Helium – Colorless and Odorless. 3 – Li – Lithium – Low Melting Point and Low Density. 4 – Be – Beryllium – High Thermal Conductivity and Non Magnetic.
Pressure would be my best guess, since no choices were given.