Dear Prof.Wong,
I am deeply sorry to inform you that I did not complete the task you designated last week, due to a sudden illness falling upon me these days. For the last week, I have been in a hospital with a continuous fever, which prevented me from any activity.
To make up my fault, could you please extend my deadline to next Friday? If so, I promise I will finish the task and send my report to you via email.
I do apologize again for any inconvenience it might bring to you, and hope you could accept my apology.
Sincerely yours,
LiMing