A：
B：
C：
D：
对于函数f（x）=2sinxcosx，下列选项中正确的是（ ）
某化学兴趣小组为了测定当地的石灰石（主要成分是CaCO3）的质量分数，他们做了如下实验：取24克样品放入烧杯中，向其中逐渐加入100克一定质量分数的稀盐酸（杂质不溶于水也不与酸反应），所用盐酸的质量分数与剩余固体的质量关系如图20所示，请根据图中的数据进行计算：
24克石灰石样品与盐酸充分反应后最多产生二氧化碳的质量为 ____ 克。
（3）求所用盐酸的溶质质量分数。（请根据化学方程式写出完整的计算步骤）
Do you have the ability to live cheaply? Now here's a true story of an American girl，Sarah．1Sarah left university，she began to live in New York City on her own．She 2 a job in a publishing house，but the salary(薪水)was 3 $30，000 a year．Her parents thought her life would be hard，but Sarah 4live on her salary and still saved $5，000 in a year．How was that 5 in one of the most expensive cities in the world? Cheap living 6starts with keeping the big cost small．For most people，that 7housing．So Sarah chose to share a flat with three other friends．Her next biggest cost was 8．When she ate out，she went to cheap restaurants．9 she bought a $9．99 whole chicken at a local restaurant．She then10the chicken bones(骨头)home and made soup out of them．Nowadays young people often 11 a lot of money on entertainment(娱乐)．But Sarah said，"I enjoy walking 12 in New York City．I love going to museums and parks．" Did Sarah feel poor13 cheap living? Not really．She even managed to take two trips，one to the Netherlands，14to Portland． “Don't think of saving money as something15．It's a kind of game，"said Sarah．
