A:in front; at the back
B:at front; at the back
C:in front; in back
D:at the front; at the back
如图是某化学反应的微观模拟示意图,下列说法正确的是( )
-- ______ our eco-travel plan might be put off.
-- Yes, it all depends on the weather.
____是商品买卖的场所。