I'll be glad to check your answer.
You can only understand English grammar if you learn the functions (or "roles") of words within a sentence. Each kind of word that can appear in a sentence (verb, noun, object) has a name that tells you what role it plays, and what it does, just like "first baseman" tells you what role a person plays in a baseball game.
In a baseball game, the "pitcher" is only a pitcher because he throws the ball. When he ceases to throw the ball, he stops being a pitcher and becomes "unemployed." So, the words only have grammatical roles in terms of their relationship with other words within a sentence. That's why you have to understand what roles words play in order to understand grammar -- the interrelation of words within speech.
In English grammar, a "subject" is a word that tells you "who" or "what" does something. It is the "subject" because it does something. In the examples above, "I" is a subject, because "I" "walked." "Walked" is doing something and whomever did it is the subject of the sentence.
A "verb" is a word that tells what action was taken "Walked" is a verb because it expresses an action. The word "walked" has no meaning except when you know WHO walked. And the word "I" conveys nothing without a verb to tell you what "I" did.
The "direct object" is a word that tells you who or what is receiving the action.
For instance, the example, "He hit the ball." "He" tells you who engaged in an action, so "he" is the subject.
"Hit" expresses action, so "hit" it is the verb in the sentence. "Ball" is the object that received the action, which you can tell if you watch the ball flying away. So, ball of the "direct object."
Another example. "The man kissed the woman." "Kissed" is the verb, since it's the word that expresses action. "Woman" is the "direct object" because that's the word that tells you who received the action.
If you apply this analysis to your sentences above, you will have no trouble seeing which sentence has a "subject" (person or persons who does something), and a "verb" (action), and a "direct object" (someone or something that was acted upon).
To answer this question you have to not simply understand the interactions between words, but you must understand the names for words that perform particular roles within a sentence. It's like studying medicine and having to learn the names of all of the bones and how they are connected to one another, and how the leg bone moves the foot bone.