关于磁场和磁感线，下列说法正确的是(    )

体液中的杀菌物质（溶菌酶）和吞噬细胞是人体第____道防线的组成．

    Now you are in a dinosaur ____park. Coming here, you will find a kind of old ____, dinosaur, which died out millions of years ago. In our park, we are happy to show you ____ dinosaurs, which lived in the Jurassic. The four-storied-building-high grass-eating dinosaurs are submissive (温顺的) and kind. You can ____ towards them and touch them. But the ____  of them are dangerous. The four-legged meat-eating dinosaurs are very cruel. Please don't ____ them and don't try to give them food. The ____ here is very thick and full of all kinds of animals that lived in the Jurassic. Without any special____and the leading of the guide, please don't step into it. OK, I'm sure that our park will ____anyone who comes here and you will ____a lot from it.