A : - can you water that plant? i'm very busy now
     - water that plant please!
     - would you help me to water that plant?
B : - of course, why not
     - sure
     - no, i can't
     - sorry i can't do it because i'm very busy now
Q: -Would you like to have lunch here?
-Culd I give you a glass of tea?
-Allow me to offer you a glass of tea

A: -Sure, thanks
-Of course
-sorry but i'm not thirsty