Why is an index contour different from other contour lines?

Witch one is it soo it the the question b.a,b,c,d

Whats the biggest sea in the world?

What must happen for new french words to be published in official dictionaries? a. they must be approved by the french academy b. they must be voted on by the people of france c. they must be used by famous french writers d. they must be used by philosophers a. they must be approved by the french academy