Baby hippopotami typically weigh between 50-60 pounds (25-30 kg) at birth, making option A correct. Hippos are large mammals and give birth to relatively sizable calves that can swim immediately after birth.选项B和C明显是干扰项 - 小河马不会唱歌,通常与母亲在一起生活。河马是独居动物,幼崽由母亲照顾。