Mammals first appeared during the Mesozoic Era. The correct option among all the options that are given in the question is option "c". The Mesozoic Era is considered to have lasted for about 180 million years. The Mesozoic Era is divided into three parts and they are the Triassic, the Jurassic and the Cretaceous. The mammals are considered to have evolved during the Triassic period.
Answer:
B: The expansion of slavery into land gained from the Mexican Cession
Its B.
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