The world's oceans are salty because the water has dissolved salt from rocks. Streams and rivers flowing over rocks for eons have carried the salt to the sea. Also, water on the ocean floor flows into thermal vents, where it becomes heated and dissolves salt from the oceanic crust. Finally, water in the vicinity of submarine volcanoes dissolves salt from the molten lava.
a Nonargument.
b Argument; conclusion: The world’s oceans are salty.
c Argument; conclusion: The water has dissolved salt from rocks.
d Argument; conclusion: Streams and rivers . . . salt to the sea.
e Argument; conclusion: Water in the vicinity . . . molten lava.