The number of tigers in the wild has increased due to conservation efforts.

由于保护努力，野生老虎的数量增加了。

同一单元的其他句子

• Wildlife protection is essential for maintaining ecological balance.野生动物保护对于维持生态平衡至关重要。
• Many endangered species are on the verge of extinction.许多濒危物种正濒临灭绝。
• We should not buy products made from ivory.我们不应该购买象牙制品。
• How can we help protect the habitats of wild animals?我们怎样才能帮助保护野生动物的栖息地？
• The government has established several nature reserves.政府已经建立了几个自然保护区。