Which words in the sentence make up the prepositional phrase?

the grocer whistled as he placed the heavy watermelons on a sturdy table.

a.
the grocer whistled

b.
as he placed

c.
on a sturdy table

d.
the heavy watermelons

evertheless he ought to be slow to believe and to act, nor should he himself show fear, but proceed in a temperate manner with prudence and humanity, so that too much confidence may not make him incautious and too much distrust render him intolerable.

explanation: