What reason does Solarino give as the probable cause of Antonio's melancholy?

The answer to this question can be found in Act 1, Scene 1 of Shakespeare's The Merchant of Venice. The scene begins with Solarino and Solanio trying to offer reasons for why Antonio's mood is down and depressing. Solarino offers the first suggestion. He thinks that Antonio is depressed because he is worried about his financial venture that involves some ships that are at sea. Solarino and Solanio both state that Antonio stands to lose quite a bit of money if those ships are lost at sea; however, Antonio responds by saying that is not the reason. He is financially well off enough in a variety of different areas that he can withstand the loss of the ships. Solanio then suggests that Antonio is feeling melancholy because he is in love.