ficus benjamina lose leaves
 

two of my f.b have lost all their leaves ON THE SAME DAY???
theit place wasn't changed...they were watered as usually but their leaves
didn't turn yellow...they just dryed out???
where's the problem???
can I do anything to save them??
temp is around 15-20°c and spring has just came!!!!
I don't get it...
help please
ivan
croatia
zone7-8