The rules don’t come right out and say that a monk can’t
use an unarmed strike for an off-hand strike (although the exact
wording of the unarmed strike ability suggests otherwise), and
no compelling reason why a monk could not do so exists.
When using an unarmed strike as an off-hand attack, the monk
suffers all the usual attack penalties from two-weapon fighting
(see Table 8–10 in the Player’s Handbook) and the monk adds
only half her Strength bonus (if any) to damage if the off-hand
unarmed strike hits.
那這一段又如何理解?