"An" is an article and has no bearing on whether a sentence is active or passive. It can be used in both active and passive voice.
An active voice sentence contains a subject who performs the action--Bobby ate an apple. In a passive voice sentence, the subject is acted upon by the verb--An apple was eaten by Bobby.
A, an, and the (Articles) are related to nouns by modifying them. Nouns may be used as subject of a sentence, an object to a verb or a preposition, or as an adjective. Nouns, together with their articles typically represent a noun phrase, and together are often either the subject or object of a sentence.
No, this sentence is written in passive voice: He was appointed to the team by his supervisor. Active voice: His supervisor appointed him to the team.
The sentence "Sentences can be written in active and passive voices" is a declarative sentence written in passive voice.
Sentences written in active voice are clearer and more straightforward than those written in passive voice. In active voice, the subject is doing something rather than having something done to them. An example of passive voice is, "He was reading the book his cousin had written." Active voice may read, "He's reading the book his cousin wrote."
active voice
change into active voice this essay was written by him
That sentence is written in active voice, despite being somewhat ambiguous.
The active voice.
"The gates were lowered by the footmen" is not in active voice. An equivalent phrase using the active voice would be "The footmen lowered the gates".
That sentence is written in active voice. "The safety features of the plane were described by the the flight attendant" is passive voice.
No.
No. Every verb in the sentence given is in the active, not the passive, voice
First, "stone like" should be hyphenated: "stone-like." The sentence as written is in active voice. If it were written in passive voice it would be: "Stone-like structures are built by corals."