Sentence Correction

Arteriviruses are a genus of microorganisms that cause digestive and respiratory infections, sometimes benign and sometimes severe, in humans, other mammals, and birds.

(A) Arteriviruses are a genus of microorganisms that cause digestive and respiratory infections, sometimes benign and sometimes severe, in humans, other mammals, and birds.
(B) Arteriviruses are a genus of microorganisms that causes digestive and respiratory infections, sometimes benign and sometimes severe, in humans and other mammals, and in birds.
(C) Arteriviruses are a genus of microorganisms that cause digestive and respiratory infections that are sometimes benign and sometimes severe, in humans, other mammals, and in birds.
(D) Arteriviruses are a genus of microorganisms, which cause digestive and respiratory infections that are sometimes benign and sometimes severe, in humans, other mammals, and birds.
(E) Arteriviruses, a genus of microorganisms, cause digestive and respiratory infections, sometimes benign and sometimes severe, in humans, other mammals, and in birds.

ardz24 wrote:Arteriviruses are a genus of microorganisms that cause digestive and respiratory infections, sometimes benign and sometimes severe, in humans, other mammals, and birds.

(A) Arteriviruses are a genus of microorganisms that cause digestive and respiratory infections, sometimes benign and sometimes severe, in humans, other mammals, and birds.
(B) Arteriviruses are a genus of microorganisms that causes digestive and respiratory infections, sometimes benign and sometimes severe, in humans and other mammals, and in birds.
(C) Arteriviruses are a genus of microorganisms that cause digestive and respiratory infections that are sometimes benign and sometimes severe, in humans, other mammals, and in birds.
(D) Arteriviruses are a genus of microorganisms, which cause digestive and respiratory infections that are sometimes benign and sometimes severe, in humans, other mammals, and birds.
(E) Arteriviruses, a genus of microorganisms, cause digestive and respiratory infections, sometimes benign and sometimes severe, in humans, other mammals, and in birds.

and must serve to connect PARALLEL FORMS.
B: in humans and other mammals, and in birds
C and E: in humans, other mammals, and in birds
In each of these options:
The two red phrases = PREPOSITION + NOUN.
The blue phrase = NO PREPOSITION + NOUN.
The result is a lack of parallelism.
Eliminate B, C and E.

D: microorganisms, which cause digestive and respiratory infections
This wording implies that ALL microorganisms cause digestive and respiratory infections.
Not the intended meaning.
The intended meaning is that only certain microorganisms -- ARTERIVIRUSES -- cause digestive and respiratory infections.
Eliminate D.

The correct answer is A.