Foreigners often make some strange mistakes in Chinese when they study the most difficult language--- ---Chinese. We try to analyze typical sentences to correct these errors.
Zuótiān tāmen fǎnɡwèn le yí ɡè ɡōnɡchǎnɡ.
Zuótiān tāmen cānɡuān le yí ɡè ɡōnɡchǎnɡ.
In Chinese, 访问 means to visit and talk with someone for a purpose. It usually requires a personal noun as its objects. To say "visit China" implies not only a tour but also talks or discussions with people concerned. The object of the sentence is 工厂 which in fact indicates the state of the factory. 参观 is the matching word for 工厂.