5.29Why B° leads to C

B°:

B D F

C:

C E G

Every note can move upward:

B → C

D → E

F → G

Or more conventionally:

B → C

F → E

D → C/E/G depending on voicing.

It has strong dominant character.

Compare:

G7 = G B D F

and:

B° = B D F

Again, B° is contained inside G7.