A：条件(1)充分，但条件(2)不充分．
B：条件(2)充分，但条件(1)不充分．
C：条件(1)和(2)单独都不充分，但条件(1)和条件(2)联合起来充分．
D：条件(1)充分，条件(2)也充分．
E：条件(1)和条件(2)单独都不充分，条件(1)和条件(2)联合起来也不充分．
设集合A={1，2}，B={1，2，3}，分别从集合A和B中随机取一个数a和b，确定平面上的一个点P(a，b)，记“点P(a，b)落在直线x+y=n上”为事件Cn(2≤n≤5，n∈N)，则事件C概率最大．
(1)n=3；(2)n=4．
参考答案：
D
解析：
(1)n=3时，P(a，b)落在直线上的点有(1，2)，(2，1)，C3=
；
(2)n=4时，P(a，b)落在直线上的点有(1，3)，(2，2)，
．故答案为D．
| The Boat On my path to the great distant mountain peak, I came to a wide river. Looking far to the right and the left, I saw no 1 , and pondered how to cross. Suddenly a pretty little 2 appeared, came to the shore and offered to take me across, to 3 me in completing my journey. The trip started 4 , and I was pleased with the little boat, and 5 for the assistance it provided. There were a few areas of 6 waters, one that even spun us around a few times, but presently we reached the far 7 . The trip had been so 8 , my gratitude and happiness so full, that I 9 to leave that little boat, even though I knew I must, to continue my journey. Much as I wanted to 10 , to spend more time drifting on the river in that little boat, the mountain beckoned (举手招唤), and my 11 had been set. As I 12 my journey, I kept looking back at that little boat with deep 13 . It had been so pleasant and had 14 me across the great river; I had grown to 15 that boat deeply. Yet I knew that the boat had its 16 in the river, and that it couldn't follow my path to the mountain. 17 I tried to take that boat along, it could not have made the journey with me, and would have stopped my own 18 . And as I watched, the little boat turned around and went back to the far shore, there to assist yet another 19 the path to the mountain. And I realized how"all 20 together for good", for each part of this magnificent universe perfectly plays its role in assisting all other parts. | ||||
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