体液中Ca²⁺含量太低时，神经、肌肉的兴奋性升高而出现抽搐,说明Ca²⁺的作用之一（    ）

Because he thinks it is good for her ____ (spend) more time with her friends.

阅读下面这首古诗，回答下面两题。
                                                                                                                                            闽中秋思
                                                                                                                                      （唐）杜荀鹤
                                                                                                                      雨匀紫菊丛丛色，风弄红蕉叶叶声。
                                                                                                                      北畔是山南畔海，只堪图画不堪行。

2008年，我国的桑蚕育种专家讲水母的绿色荧光蛋白基因转移到桑蚕的体内，培育出能产生绿色荧光蚕丝的新品种。这项现代生物技术称为（　　）