New Year's Day is coming. The students in Class 8 are preparing for a New Year's party. Cindy and Mary are malting red paper birds They want to put them outside (在……外面) the classroom  Lily and Alice are cleaning the desks and chairs They want a clean classroom. There are some pictures on the walls and there are also some beautiful flowers on the desks. Some boy students are learning taijiquan in the playground. They want to show (展示) it at the party. Where are Jack and Nancy? Oh, they are still in the shop. They are buying some food and drinks for the party. "We are very happy because we can have a big party," says Mike, the monitor (班长).

某国发现在其境内的老虎经常遭人猎杀．若不采取措施，老虎有灭绝的可能，于是采取下列措施，请问哪些措施是正确的（　　）

①在栖息地引进狮群和豹群②在栖息地保持一定数量的牛群和羊群③在栖息地建立自然保护区④制定法律，严禁捕猎老虎．

一质子束入射到能止靶核 ${}_{13}^{27}$ AI上，产生如下核反应：P+ ${}_{13}^{27}$ AI→X+n式中p代表质子，n代表中子，X代表核反应产生的新核．由反应式可知，新核X的质子数为____，中子数为____．