Which of the following sentences is written in the passive voice?
a. the effects of cyanide are well known.
b. they considered their options.
c. having left the building, elvis never returned.
d. i would not provoke that man if i were you.

The correct answer is

 a. The effects of cyanide are well known.

This is because the active voice to this would be "Humans know the effect of cyanide" which turned into the passive form of "The effects of cyanide are well known

Explanation:

One of the 2 “voices” of verbs (see additionally active voice). A verb is within the passive once the topic of the sentence is acted on by the verb. for instance, in “The ball was thrown by the pitcher,” the ball (the subject) receives the action of the verb, and was thrown is within the passive.

the speech this question is referring to is president kennedy's special message to the congress on urgent national needs, may 25, 1961

kennedy responds in a very direct and concrete way to those thinking that communism is a positive system:

"yet their aggression is more often concealed than open. they have fired no missiles; and their troops are seldom seen. they send arms, agitators, aid, technicians and propaganda to every troubled area. but where fighting is required, it is usually done by others--by guerrillas striking at night, by assassins striking alone--assassins who have taken the lives of four thousand civil officers in the last twelve months in vietnam alone--by subversives and saboteurs and insurrectionists, who in some cases control whole areas inside of independent nations." (kennedy)

president kennedy presents communism as cowardly, as a hidden and treacherous weapon that strikes from the shadows like thieves, he represents the system as not even being capable of showing and open and overt attack or confrontation. to finish up the response, he expresses that the system attacks even a country's idependence and freedom.

could you put the choices and excert up hun