写作思路：根据题目要求，围绕大象展开描写。
Elephant is the largest terrestrial mammal in the world. It is usually a family unit. Sometimes several elephants gather together to form hundreds of elephants.
大象是世界上最大的陆生哺乳动物，通常是一个家族单位，有时几头大象聚集在一起形成数百头大象。
The cortex is very thick, but the skin is very thin, so it is often used to prevent mosquitoes from biting.
皮层很厚，但皮肤很薄，所以经常用来防止蚊虫叮咬。
Ivory is an important weapon against the enemy.
象牙是对抗敌人的重要武器。
The ancestors of elephants appeared on earth tens of millions of years ago.
大象的祖先在几千万年前就出现在地球上。
Elephant family has been very prosperous, is one of the most important animal groups on earth, more than 400 fossils have been found.
大象家族一直非常繁荣昌盛，是地球上最主要的动物类群之一，已发现400多种化石。
However, due to the influence of historical climate and human factors, there are fewer and fewer ethnic groups.
但由于历史气候和人为因素的影响，导致民族类型越来越少。
At present, there are only 2 genera and 3 species of Asian elephant, African elephant and African forest elephant on the earth, which are also facing serious threat.
目前，地球上只有亚洲象、非洲象、非洲林象等2属3种，也面临着严重的威胁。