In this first sentence, we have a clear case of subject followed by predicate without any elements in between them that would require commas or any other punctuation mark. In the second sentence, the comma between the subject clause "Why Eric dropped the ball" and the predicate "is anyone's guess" should not be there. In the third sentence, a comma must be added after "When the bell rings," since this is an adverbial clause at initial position, which are always followed by a comma.
The transition words I have used to alter the following paragraph are in CAPS.
Darius went to the store BECAUSE he wanted food. WHILE shopping, he ran into his teacher AND they talked about his latest project, WHICH he decided to base on gourmet cooking.
Ben flies a kite during a thunderstorm and collects ambient electrical charge in a jar for him to demonstrate the connection between lightning and electricity.
