英文 from 問題

prevents the ex-employee from dealing with customers of the business by using knowledge of those customers gained during his prior employment

防止前僱員使用前受僱期間所獲得有關這個行業的客戶知識，去與這些客戶交易。

In English grammar, certain verbs must work together with certain prepositions in order to represent specific meanings.

For Example:

Prevent [somebody] from [doing somethig]. 防止某人(去)做某些事情。
Stop [something] from [happening]. 阻止某些事情 (去) 發生。
Encourage [somebody] to [do somethig].鼓勵某人(去)做某些事情。
Allow [something] to [happen].准許某些事情 (去) 發生。

Note that in English grammar, [from] is used with [prevent] and [stop], whereas [to] is used with [encourage] and [allow]. In Chinese grammar, however, the meaning of the preposition [to] and [from] are already included in the meaning of these verbs, such that only the preposition [去] is needed, for all the four verbs - 防止, 阻止, 鼓勵, 准許。(*note that the use of [來 ] and [去 ] is relevant, in Chinese grammar, for certain verbs, such as "running from" & "running to" [跑來跑去]).

Therefore, in the subject sentence, the function of "from" is to act as a preposition, to work with the verb "prevent", and to allow the items so prevented, to be listed behind it. The meaning of "from", is [去], but it has to be paired with the meaning of the governing verb, such that [prevented from] = 防止去.