如下图所示。将4株相同的蚕豆幼苗分别放在4个暗箱中一段时间，其中2号和4号暗箱分别在顶部和右侧开孔，使光线能射入。如果要研究光与茎生长的关系，可选择的装置是（）
A．②和④
B．③和④
C．①和②
D．①和③
参考答案：B
解析：由题目可知，该实验的自变量是是否照射单侧光，重力等其他影响茎生长的因素均为无关变量，为了排出重力对幼苗生长方向的影响，所以蚕豆幼苗应该竖直放置。故B正确考点：本题考查影响植物向光性的因素和实验设计原理的相关知识，意在考查考生实验设计能力。
阅读下面短文，掌握其大意，然后从36—55各题所给的四个选项（A、B、C和D）中，选出最佳选项。 I am a mother of three and have recently completed my college degree. My teacher’s last 36 of the term was called “ Smile”. I am a very friendly person and always 37 at everyone. So I thought this would be very 38 . Soon after we were given the project, my 39 went out to McDonald’s. We were waiting to be 40 , when all of a sudden everyone around us began to 41 , and even my husband did. There standing behind me were two homeless men 42 . As I looked down at the short gentleman with 43 eyes, he said, “ Good day.” The second man stood behind his friend. I 44 the second man was mentally challenged（智障）and the blue-eyed gentleman was his helper. The young 45 at the counter asked him what they wanted. He said, “ Coffee is all ,Miss.” Because that was all they could 46 . I smiled and asked the young lady to give me two more breakfast meals on a 47tray（托盘）. I then said to the men, “ I did not do this for you. God is here 48 through me to give you hope.” When I joined my husband, he smiled at me, saying, “That is 49 God gave you to me, Honey, to give me hope.” I returned to 50 with this story in hand. I 51 “my project” and the teacher read it. Then she looked up at me and said, “ Can I 52 this with the class?” I slowly 53 and she began to read and that was when I knew that we, as human beings, share this to help people and to be 54. In my own way I had 55 the people at McDonald’s, my husband, sons, teacher, and every person that shared the classroom on the last night I spent as a college student.
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