The correct answer is: B. Millibars or hectopascals.
Millibars (mb) or hectopascals (hPa) are the units of pressure most commonly found on a surface weather map. They are used to measure the weight of the air above a given point on Earth’s surface. The higher the pressure, the heavier the air and the more stable the atmosphere. The lower the pressure, the lighter the air and the more unstable the atmosphere.
A. Inches of mercury (Hg) is a unit of pressure that is still used in some countries, but it is not as common as millibars or hectopascals.
C. Pounds per square inch (psi) is a unit of pressure that is used in engineering and other fields, but it is not commonly used on weather maps.
D. Millimeters of mercury (Hg) is a unit of pressure that is equal to 0.1333 millibars. It is sometimes used in scientific studies, but it is not commonly used on weather maps.