题目

 The cost of organic food is higher than ___________ of conventional food because the organic price tag reflects more closely the true cost of growing the food． A. it                            B. one                C. this                        D. that 答案：D如图，在长方体ABCD-A′B′C′D′中，DA=DC=2，DD′=1，A′C′与B′D′相交于点O′，点P在线段BD上（点P与点B不重合）．（1）若异面直线O′P与BC′所成角的余弦值为5555，求DP的长度；（2）若DP=322，求平面PA′C′与平面DC′B所成角的正弦值．