Answer for a,b,c,d

Dear Student, 

a. if he knew that the Christmas party scheduled for the week after had been called off.
b. in the affirmative
c. it had been called off to pay our respects to the people who had died in the landslide that had occurred near Manali.
d. could collect enough money to contribute towards the funds that was being collected for the victims. 

Regards,