题目

纯合黄色圆粒豌豆与绿色皱粒豌豆杂交，F1都为黄色圆粒豌豆，若遵循自由组合定律，理论上F2中纯合子所占比例及通过性状就能识别出的纯合子所占比例分别是（ ） A．、   B．、      C．、   D．、 答案：解：由以上分析可知，亲本的基因型为YYRR×yyrr，F1的基因型为YyRr． （1）根据基因自由组合定律，F2中纯合子所占比例为； （2）F2中纯合子的基因型及概率为YYRR、YYrr、yyRR、yyrr，在这四种表现型中，通过性状能识别出属于纯合子的只有双隐性个体，占F2的． 故选：D． That cold January night, I was growing sick of my life in San Francisco. There I was, walking home at one in the morning after a tiring    at the theatre. With opening night only a week away, I was    learning my lines. I was having trouble    my part-time job at the bank and my acting at night at the same time. As I walked, I thought seriously    giving up both acting and San Francisco.    had become too much for me. As I walked down    streets under tall buildings, I felt very    and cold. I began running, both to keep warm and to keep away from any possible robbers. Very few people were still out except a few sad-looking homeless people under blankets. About a block from my apartment, I heard a sound behind me. I turned   , half expecting to see someone with a knife or a gun. The street was empty.    I saw was a shining streetlight.   , the noise had made me nervous, so I started to run fast. Not until I reached my apartment building and unlocked the door did I realize what the noise had been. It had been my wallet falling to the sidewalk.   I wasn’t cold or tired anymore. I ran out of the door and back to    I’d heard the noise.    I searched the sidewalk anxiously for fifteen minutes, my wallet was nowhere to be found. Just as I was about    the search, I heard the garbage truck pull up to the sidewalk next to me. When a voice    from the inside. “Alisa Camacho?” I thought I was dreaming. How could this man know my name? The door opened, and out jumped a small red-haired man with an     look in his eyes. “Is this what you’re looking for?” he asked,    a small square shape. It was nearly 3 a. m. by the time I got into bed. I    get much sleep that night, but I had gotten my wallet back. I    had gotten back some enjoyment of city life. I realized that the city couldn’t be a bad place    people were willing to help each other. 1.A. exercise            B. work             C. practice                          D. training 2.A. still                     B. already                  C. yet                                   D. only 3.A. to deal with      B. to handle with     C. handling with                D. dealing with 4.A. of                        B. about                     C. over                                D. out 5.A. City life              B. Country life          C. School life            D. Modern life 6.A. busy                            B. crowded               C. noisy                      D. empty  7.A. proud                B. confident              C. small                      D. excited 8.A. fast                              B. immediately         C. rapidly                            D. quickly 9.A. All which                    B. All                          C. That                                 D. Which 10.A. Therefore                B. Still                         C. Consequently                D. Subsequently 11.A. Suddenly                  B. Gradually     C. Absolutely            D. Exactly 12.A. which              B. that                        C. where                             D. what 13.A. Even if             B. Although               C. As if                       D. As though 14.A. to give in                  B. giving in                C. to give up             D. giving up 15.A. called              B. calling                    C. was called             D. to call 16.A. amusing                    B. amazing      C. amazed                           D. amused 17.A. to hold up                B. holding up  C. to hold on                     D. holding on 18.A. couldn’t                    B. wouldn’t               C. didn’t                              D. shouldn’t 19.A. still                            B. already                  C. also                                 D. certainly 20.A. as far as                    B. as well as     C. as soon as             D. as long as