a) b) I believe there's a slight difference between 'already' and yet':Originally Posted by Emanuelli
'Have you already had a shower? (the speaker's asking if it has actually happened)
'Have you had a shower yet?' (the speaker is expecting it to happen)
But 'yet' is mainly used in negative sentences.
c) To hold students' attention = (in order) to hold students' attention...cause-effect situation. If you drop it out, this would become an imperative situation.
d) 'will you' is OK.
This is what I think..but I'm not a 100% reliable source!