1.
create trigger testA on A
for insert
insert B(a1,a2)
select a1,a2 from inserted
2.
create trigger testB on A
for delete
insert B(a1,a2)
select a1,a2 from delete
3.
create trigger testC on A
for update
insert B(a1,a2)
select a1,a2 from deleted
insert B(a1,a2)
select a1,a2 from inserted