Question

what are isobars?
lines on a weather map that connect places of equal wind speed
lines on a bar graph showing pressure measurements
lines on a weather map that connect places of equal pressure
lines on a weather map that connect places of equal temperature

Explanation:

Isobars are lines on a weather map. Their key characteristic is connecting places. The specific connection is based on equal pressure.

Answer:

lines on a weather map that connect places of equal pressure