可使人致病的有毒化学物质引起的危害属于（）。
A.病毒性危害
B.生物性危害
C.物理性危害
D.化学性危害
参考答案：D
若a、b、c是△ABC的三边，a+c=2b，且方程a（1-x2）+2bx+c（1+x2）=0有两个相等的实数根，sinA+sinB+sinC的值．
Each member country WTO must ___________ its laws and regulations and compete on the principle of fairness and cooperation.
A．submit to
B．cater to
C．correspond to
D． relate to
