Which is not a property of magnetic field lines?

a.
they form complete loops from pole to pole.
b.
they can be directly observed.
c.
they never cross.
d.
they spread out as they get farther from the magnet.

the sugar-phosphate backbone forms the structural framework of nucleic acids, including dna and rna. this backbone is composed of alternating sugar and phosphate groups, and defines directionality of the molecule.

actually the answer is c