1.count up swans' number / count swans' number up / add up swans' number / add swans' number up / worked out swans' sum / figure out swans' sum
【注】:count up the number of sth.=count sth.给…计数;worked out / figure out sth.' sum 计算…的总数
2.in danger
【注】:endangered =in danger,endangered作前置定语,in danger作后置定语
3.be no / exist no
【注】:There is =There exists,There are=There exist.
语法上都是对的,请根据与课文的相关度选择最佳项.