美国南北战争爆发前，两种经济制度的矛盾十分尖锐，这两经济种制度是北方资本主义经济和南方种植园奴隶制经济。[ ]
√
When you finished a piece of writing, check that that the tenses are consistent and the
spelling is correct.
A, they are making senses B, it makes sense
C, it makes senses D, they make sense
约束超导现象的三大条件是（）、（）和（）。
