Statements: All oceans are rivers. Some springs are rivers. All wells are springs. Conclusions:  Some springs are oceans. Some wells are rivers. Some rivers are oceans. No well is river.

III is the converse of the first premise and so it holds.

All oceans are rivers. Some springs are rivers.

Since the middle term 'rivers' is not distributed even once in the premises, no definite conclusion follows.

All wells are springs. Some springs are rivers.

Since the middle term 'springs' is not distributed even once in the premises, no definite conclusion follows. However, II and IV involve the extreme terms and form a complementary pair. Thus, either II or IV follows.