题目

根据短文理解，选择正确答案。 People have smoked cigarettes for a long time now. The tobacco which is used to make cigarettes was first grown in what is now part of the United States. Christopher Columbus, who discovered America, saw the Indians smoking. Soon the dried leaves were transported to Europe. In the late 1800s, the Turks made cigarettes popular. Cigarette smoke contains at least two harmful substances, tar and nicotine. Tar, which forms as the tobacco burns, damages the lungs and therefore affects breathing. Nicotine, which is found in the leaves, causes the heart to be血液中有一种含铜的呈蓝色的蛋白质分子，其相对分子质量约为151000。已知该分子中铜的质量分数为0. 34%，则平均每个蛋白质分子中的铜原子数为 [     ]A．8 B．6 C．4 D．2