题目

Taking a math test can be pretty stressful. Even if you know the material, you can still get the problem wrong. ___16___ Therefore you’ll improve your grades, as well as your math skills. Write it out You can also check a math problem by writing everything out on paper. ___17___ Writing out math problems reduces your chances of missing anything to the lowest possible level, which is a common cause of incorrect answers. ___18___ Make sure your answers work by doing the opposite procedure of what your problem calls for, including the answer you got the first time around. In other words,在植物根尖的结构中，终生保持分裂能力的是（ ）A．根冠B．分生区C．伸长区D．成熟区