Sentences: Beginning a sentence

Marnqui was on his way to the park when he met Lil' Pompurse walking hurriedly toward the bus-stop.

Marnqui:	Hey, wait up, where are you off to?
Lil' Pompurse:	(With his little chest puffing up in a proud heave) I am off to tutor my classmates on what makes a sentence and what does not?
Marnqui:	Wow, so you are now a tutor?
Lil' Pompurse:	Yup, I am the smartest in class, so Mr John told me to help the others.
Marnqui:	Oh, pray then, tell me, what makes a sentence a sentence and what does not?
Lil' Pompurse:	Hmmm, so you don't know either, huh? (The chest heaved even more!)
Marnqui:	Don't bother about what I know or don't, just tell me, what are you going to teach your classmates?
Lil' Pompurse:	Well, it usually starts off with the subject or doer of the action. You know, like `I had cereal for breakfast.' The `I' is the subject or the one in the thick of the action!
Marnqui:	Oh, alright... then, what about a sentence that starts with an object?  What would your answer be for a sentence that goes like this: `The cereal was eaten by me.'
Lil' Pompurse:	I am coming to that! (Here, the chest deflated a little, but just for a moment, mind you!) That would depend on whether the sentence is an active or passive voice.
Marnqui:	Voice?! You mean, a sentence talks?!
Lil' Pompurse:	(Breaking into spirited laughter, or to our texting friends, lol) Gosh, you crack me up! In an active voice, the focus is on the subject or doer and the action, so the sentence is, sort of, active, you know. From my given example, the focus is on the `I' having the cereal. However, in the case of the passive voice, the attention is drawn to the object, or the recipient, or result, of the act. Thus, in your example, you want people to pay attention to the cereal and not the `I' or subject. Hence, you said, `The cereal was eaten by me.' Both are correct. It just depends on what or whom you want to draw attention to.
Marnqui:	Wow, you are so smart, Pompurse! Now, do you see this sign? What do you make of it? Some of these sentences don't start with a subject or an object? So, are they proper sentences?

What do you think? Are they `proper' sentences? Answers from The Pear Tree Centre for Education coming soon.

Meanwhile, look out for the additional exercise on complete and incomplete sentences, which will be available in a couple of days.