where one massive tributary, the Rio Negro, flows into the main river. 一条巨大的支流 ——内格罗河在此汇入干流
Rising in the Peruvian Andes, its main trunk flows eastwards across Brazil. 它发源于秘鲁安第斯山区 其干流穿越整个巴西
The main herd has already got there safely. 大部队早已安全抵达
Females and calves can easily get separated from the main herd. 母象和小像一不小心就会和大部队分开