因为x=5y，
所以xy=5（一定），
即x与y的乘积一定，
所以x和y成反比例，
故选：B．
--Can you come to the welcome party for our new friend next Saturday night?
--_______.
A．Sorry, I won’t.
B．Sure, I’d love to.
C．Yes, I’ll go to your party.
D．Yes, I’ll have a great time at your party.
无焰燃烧和有焰燃烧的必要条件各有哪些？
