The correct answer is: [C]:
_____________________________________________________
" {I heard Charlie say that he was "head over heels in love."} " .
_____________________________________________________
The last answer sets the most formal tone; "Hello! I was very pleased to meet you at the party last week." the rest are very casual.
A reader might feel like they can relate to the situation that the writer is going through. They understand and therefor can relate emotionally to the situation.