What do the following rhyming word pairs have in common?

1. CURE - TOUR
2. MOTE - NOTE
3. BOWL - SOLE
4. VERB - SERVE
5. POUND - FOUND
6. PORTION - TORTION

HINT:
It has to so with prefixes.

Answer:

The first word in each pair can be preceded by PRO and the second by CON:

1. PROCURE - CONTOUR
2. PROMOTE - CONNOTE
3. PRO-BOWL - CONSOLE
4. PROVERB - CONSERVE
5. PROPOUND - CONFOUND
6. PROPORTION - CONTORTION

Credit: Joseph Appel