Question 16 is based on the passage you have just heard.

听力原文

        Pigs are not native to North America. They were first introduced to California by Spanish and Russian explorers and settlers many centuries ago. (16) [In the early times, pigs were allowed to wander freely in search of food. This practice also allowed many pigs to escape from farms and live in the wild, which became a problem.] In fact, they’re one of the most damaging invasive species on the continent. Wild pigs cause millions of dollars in crop damage yearly. (17) [They also harbor dozens of diseases that threaten both humans and farm animals.] Forest patches with wild pigs have been found to have considerably reduced plant and animal diversity. In addition to either eating other animals or their food supply, wild pigs damaged native habitats by rooting up grasses and rubbing on trees. Their activities may also create opportunities for invasive plants to colonize these areas. Wild pigs will eat almost anything containing calories. Mice, deer, birds, snakes and frogs are among their victims. They can also harm other wild species through indirect competition rather than eating them or shrinking their food supply. On one particular United States island, wild pigs themselves became an attractive food source for a species of mainland eagle. (18) [The eagles began breeding on the island and also feeding on a species of native fox. The foxes were almost wiped out completely.]

16. What do we learn about early pigs in North America?（关于早先北美的猪，我们了解到什么？）

解析：A。录音开头说到，刚开始，猪可以自由地四处游荡、寻找食物。这种做法也让许多猪逃离农场在野外生活，成为了一个问题。随后就讲到了野猪的不良影响。由此可知，早先，由于不受限制，农场的猪在逃跑之后变成了野猪。A项与此内容相符，其中的escaped from farms为原词复现，became wild对应录音中的live in the wild，故A项为正确答案。

错项排除：录音开头提到猪并非原产于北美洲，B项与此内容相悖，故错误。录音中提到猪在早先是可以自由地四处游荡、寻找食物的，C项与此内容相悖，故错误。录音中虽然提到了西班牙和俄罗斯的探险家，但说的是他们将猪带到加利福尼亚州，而不是猎杀它们，故D项错误。