What is the imaginary line called that connects the north and south pole?

Question

On the map, what line connects the places having equal average atmospheric pressure ?
(A) Isobar
(B) Isochrone
(C) Isotherm
(D) Isohalines

Answer 1

Longitudes

Longitudes are imaginary half circles (though it feels like straight line but its actually half circle) that connects the North and South Poles.