题目

“唾液对淀粉的消化实验”要求在一定温度进行，这是由于唾液中的淀粉酶在高于和低于37℃条件下催化作用都会逐渐降低．下图能正确表示唾液淀粉酶的作用与温度关系的是（ ）A.     B. C.     D. 答案：【答案】D【解析】试题分析：唾液淀粉酶的消化作用应该是随着温度的逐渐升高，消化作用逐渐增强，达到一定温度后（37℃），随温度升高，消化作用又逐渐减弱，即呈一弧形曲线．故选：D完形填空阅读下面短文，从短文后各题所给的四个选项（A.B.C和D）中，选出可以填入空白处的最佳选项，并在答题卡上将该项涂黑。On a trip to California, my family stopped for lunch. As we walked toward the entrance to the restaurant, a man, with a beard and dirty hair, jumped up from a bench outside the restaurant and opened the door for us．Regardless of his , he greeted us in a friendly way．Once inside, my daughters whispered, "Mom, he ." After we ordered our lunch, I explained, telling the kids to look the dirt．We then watched other customers approach the restaurant but many him. Seeing this rudeness truly upset me. The day I became a mother, I had determined to set a good to my children. Yet sometimes when things didn't go right, being a good example was . When our meal arrived, I realized I had left the car-sick pills in the truck. With the windiest trip ahead, the kids needed them, so I myself from the meal and went to get them．Just then, the "doorman" was opening the door for a couple. They rushed past him without even acknowledging his . Letting them in first, I said a loud "thank you" to him as I ．When I returned, we talked a bit．He said he was not allowed inside he purchased food．I went back and told my family his .Then I asked our waitress to add one soup and sandwich．The kids looked as we had already eaten, but when I said the order was for the "doorman" , they smiled．When it was time to our trip, I found the "doorman" enjoying his meal．Upon seeing me, he stood up and thanked me heartily. He then out his hand for a handshake and I gratefully accepted. I suddenly noticed the tears in his eyes—tears of .What happened next drew great astonishment: I gave the " doorman" a . He pulled away, with tears ________ down his face．Back in truck, I fell into deep thought. While we can't choose many things in life, we can choose when to show gratitude. I said thanks to a man who had held open a door for me, and also said thanks for that to teach my children by example．1.A. clean B. pretty C. messy D. bright2.A. service B. appearance C. state D. attitude3.A. smells B. smokes C. signs D. smiles4.A. around B. into C. over D. beyond5.A. refused B. ignored C. missed D. hated6.A. example B. target C. record D. rule7.A. accessible B. tough C. awkward D. stressful8.A. prevented B. refreshed C. forgave D. excused9.A. company B. challenge C. presence D. attack10.A. exited B. approached C. marched D. quitted11.A. before B. since C. though D. unless12.A. desire B. deed C. story D. demand13.A. puzzled B. excited C. concerned D. bored14.A. make B. start C. take D. continue15.A. washed B. reached C. raised D. waved16.A. approval B. sympathy C. gratitude D. affection17.A. clap B. nod C. lift D. hug18.A. streaming B. rushing C. slipping D. breaking19.A. firmly B. constantly C. simply D. politely20.A. opportunity B. journey C. wisdom D. community