限界分为几类，分别是哪几类？
参考答案：
限界分为3类，分别是建筑限界，设备限界，车辆限界。
They arrived at a farmhouse, in front of _____ sat a small boy. [ ]
A. whom
B. who
C. which
D. that
血浆内催化胆固醇生成脂酰胆固醇的酶是
A．ACATB．肉毒碱脂酰转移酶C．磷脂酶CD．LCAT
