调查结果表明,事故主要是人为操作失误造成的。Diàochá jiéguǒ biǎomíng, shìgù zhǔyào shì rénwéi cāozuò shīwù zàochéng de.The investigation showed that the accident was mainly caused by human operational error.
这片湖水变脏是人为造成的,不是自然现象。Zhè piàn húshuǐ biàn zāng shì rénwéi zàochéng de, bú shì zìrán xiànxiàng.This lake became dirty because of human activity, not because of a natural phenomenon.
这些困难都是人为设置的障碍,并不难解决。Zhèxiē kùnnan dōu shì rénwéi shèzhì de zhàng'ài, bìng bù nán jiějué.These difficulties are all obstacles put there by people and are not hard to solve.