胎儿和母体通过______上的绒毛进行物质交换
问题解答：
（1）∵f'（x）=x<sup>2</sup>-ax+（a<sup>2</sup>-3），函数f（x）在（-∞，+∞）上是增函数，∴f'（x）=x<sup>2</sup>-ax+（a<sup>2</sup>-3）≥0在R上恒成立．（3分）∴△=a<sup>2</sup>-4（a<sup>2</sup>-3）≤0，∴a≤-2或a≥2，即a∈（-∞，-2]∪[2，+∞）．（6分）（2）∵f（x）的单调递减区间为（m，n），且{x|x＜0}∩{m，n}≠?．∴f'（x）=0的两根为m，n且m，n中至少有一个负根．（8分）∴f'（0）＜0，或<span dealflag="1" class="MathZyb" mathtag="math" style="whiteSpace:nowrap;wordSpacing:normal;wordWrap:normal"><table style="margin-right: 1px" cellspacing="-1" cellpadding="-1"><tr><td style="font-size: 0"><div hassize="21"><div style="background: url('http://hiphotos.baidu.com/zhidao/pic/item/80cb39dbb6fd526687428ba0a818972bd407361c.jpg') no-repeat; width:9px; height:6px;overflow:hidden"></div><div style="background: url('http://hiphotos.baidu.com/zhidao/pic/item/50da81cb39dbb6fd0ba3af920a24ab18962b378d.jpg') repeat-y; width:9px; height:1px;overflow:hidden" muststretch="v"></div><div style="background: url('http://hiphotos.baidu.com/zhidao/pic/item/0eb30f2442a7d933ac2253c7ae4bd11372f001ff.jpg') no-repeat; width:9px; height:9px;overflow:hidden"></div><div style="background: url('http://hiphotos.baidu.com/zhidao/pic/item/50da81cb39dbb6fd0ba3af920a24ab18962b378d.jpg') repeat-y; width:9px; height:1px;overflow:hidden" muststretch="v"></div><div style="background: url('http://hiphotos.baidu.com/zhidao/pic/item/8694a4c27d1ed21b40119951ae6eddc450da3fad.jpg') no-repeat; width:9px; height:6px;overflow:hidden"></div></div></td><td><table style="text-align: left; width: 100%; margin-left: 1px; margin-right: 1px" cellspacing="-1" cellpadding="-1"><tr><td>△=<span><span>a</span><span style="vertical-align:super;font-size:90%">2</span></span>-4(<span><span>a</span><span style="vertical-align:super;font-size:90%">2</span></span>-3)＞0</td></tr><tr><td style="padding-top:6px"><table cellpadding="-1" cellspacing="-1" style="margin-right:1px"><tr><td style="border-bottom:1px solid black">a</td></tr><tr><td>2</td></tr></table>＜0</td></tr><tr><td style="padding-top:6px">f′(0)≥0</td></tr></table></td><td style="font-size: 0"></td></tr></table></span>，（10分）∴<span dealflag="1" class="MathZyb" mathtag="math" style="whiteSpace:nowrap;wordSpacing:normal;wordWrap:normal">a∈(-2，<table cellspacing="-1" cellpadding="-1"><tr><td style="font-size: 0px"><div hassize="7"><div style="width:6px;background: url('http://hiphotos.baidu.com/zhidao/pic/item/aa64034f78f0f736dcbbf8b50955b319ebc41338.jpg') repeat-y; height: 1px;overflow: hidden" muststretch="v"></div><div style="width:6px;background: url('http://hiphotos.baidu.com/zhidao/pic/item/c2cec3fdfc0392458726adbb8494a4c27c1e25f6.jpg') no-repeat; height: 7px; overflow: hidden"></div></div></td><td style="padding:0;padding-left: 2px; border-top: black 1px solid;line-height:normal">3</td></tr></table>)</span>，即实数a的取值范围为 <span dealflag="1" class="MathZyb" mathtag="math" style="whiteSpace:nowrap;wordSpacing:normal;wordWrap:normal">(-2，<table cellspacing="-1" cellpadding="-1"><tr><td style="font-size: 0px"><div hassize="7"><div style="width:6px;