Final answer:
The sentence 'A number of people are speaking English as a foreign language' can be transformed into the passive voice to read: 'English is being spoken as a foreign language by a number of people.' The passive voice emphasizes the subject being acted upon rather than the performer of the action.
Step-by-step explanation:
When considering the sentence "A number of people are speaking English as a foreign language" and its passive form, it is important to understand the rules of the passive voice. The passive voice occurs when the subject of the sentence is acted on by the verb. To form the passive voice, one typically uses a form of the verb "to be" along with the past participle of the main verb, and optionally, the preposition "by" followed by the doer of the action if necessary. In this case, the passive construction of the sentence might read: "English is being spoken as a foreign language by a number of people." Here, the action (speaking English) is performed by the people, but the people are not the grammatical subject of the sentence; instead, "English" is.