Answer: B. The effects of cyanide are well known.
“The effects of cyanide are well known” is a sentence written in a passive voice. A passive voice is a form or a collection of verbs where the subject present in the sentence undergoes the action of the verb. An example can be seen in the sentence “the spaghetti was eaten by him” as opposed to the sentence with an active voice “he ate the spaghetti.”