the answer is true
rules for 3NF:
for a non-trivial dependency x --> y on a relation R
1)x is a super key
2)or y is a prime attribute
rules for BCNF
for a non-trivial dependency x --> y on a relation R
x must be a super key
from thsi we can conclude that BCNF is a subset of 3NF
thus every BCNF is in 3NF, but every 3NF may not be BCNF,
because if a 3Nf just satisfies the 2nd rule it will not be in BCNF