Arteriviruses are a genus of microorganisms that cause digestive and

https://www.nytimes.com/2013/05/10/opinion/the-next-pandemic-is-closer-than-you-think.html

Coronaviruses are a genus of bugs that cause respiratory and gastrointestinal infections, sometimes mild and sometimes fierce, in humans, other mammals and birds. They became infamous by association in 2003 because the agent for severe acute respiratory syndrome, or SARS, is a coronavirus. That one emerged suddenly in southern China, passed from person to person and from Guangzhou to Hong Kong, then went swiftly onward by airplane to Toronto, Singapore and elsewhere. Eventually it sickened about 8,000 people, of whom nearly 10 percent died. If not for fast scientific work to identify the virus and rigorous public health measures to contain it, the total case count and death toll could have been much higher.

Probably the easiest decision point to assess first is the obvious subject-verb agreement choice between "cause" and "causes".

Since that relative clause is modifying microorganisms (not genus!) the verb must be the plural "cause." This allows you to eliminate (B) and (C).

Then note the other important decision point in many of these answer choices - the list at the end of the sentence.

Choices B, C, and E, all improperly list the three items that should be in parallel form: in humans, other mammals, and birds so (E) can also be eliminated.

And choice D illogically assigns "which cause digestive and respiratory infections" to all microorganisms, when the point of the sentence is to show that this particular type of microorganism, the arterivirus, is what causes those problems.

Choice A commits none of these errors, and is correct.