噎膈之证的发病机理主要是（）
A.脾胃俱伤
B.肺胃两伤
C.气血郁结
D.本虚标实
E.气痰瘀交结，阻于食道、胃脘
参考答案：E
已知一个多项式P=2a2-8ab+17b2-16a-4b+2077，当a，b为何值时，P有最小值？并求出P的最小值．
I’ll never forget such a beautiful place _____ I spent my childhood there with my grandparents. [ ]
A. because
B. where
C. which
D. when
