Brown tides are growths of algae on the sea's surface that prevent sunlight from reaching marine plants below, thereby destroying not only the plants but also the shellfish that live off these plants. Biologists recently isolated a virus that, when added to seawater, kills the algae that cause brown tides. Adding large quantities of this virus to waters affected by brown tides will therefore make it possible to save the populations of shellfish that inhabit those waters.


Which of the following, if true, provides the most support for the conclusion of the argument?



A. When applied in large quantities, the virus not only kills the algae that cause brown tides but also many harmless kinds of algae.


B. Marine animals that prey on shellfish avoid areas of the sea in which brown tides are occurring.


C. The number of different kinds of virus present in seawater is far greater than many marine biologists had, until recently, believed.


D. The presence of large quantities of the virus in seawater does not adversely affect the growth of marine plants.


E. The amount of the virus naturally present in seawater in which brown tides occur is neither significantly greater nor significantly less than the amount present in seawater in which brown tides do not occur.



Let’s look at the premises and conclusion of the argument.


Premises


Brown tides are growths of algae on the sea's surface that prevent sunlight from reaching marine plants below, thereby destroying not only the plants but also the shellfish that live off these plants.

Biologists recently isolated a virus that, when added to seawater, kills the algae that cause brown tides.


Conclusion


Adding large quantities of this virus to waters affected by brown tides will therefore make it possible to save the populations of shellfish that inhabit those waters.


We need to find an option that supports the conclusion.


A. When applied in large quantities, the virus not only kills the algae that cause brown tides but also many harmless kinds of algae.

Option A tells why adding large quantities of this virus can be problematic- because it kills many harmless kinds of algae too. Definitely doesn’t support the conclusion. Eliminate. 


B. Marine animals that prey on shellfish avoid areas of the sea in which brown tides are occurring.

The conclusion is limited to - Adding large quantities of this virus to waters affected by brown tides make it possible to save the populations of shellfish that inhabit those waters. Option B is irrelevant to the conclusion. Eliminate. 


C. The number of different kinds of virus present in seawater is far greater than many marine biologists had, until recently, believed.

Again, doesn’t support the conclusion. Irrelevant. Eliminate. 


D. The presence of large quantities of the virus in seawater does not adversely affect the growth of marine plants.

The stimulus says- 

The growth of algae blocks sunlight from reaching marine plants. Shellfish feed on marine plants. Plan- Add virus to kill the algae that cause brown tides

 

If the presence of large quantities of the virus in seawater does not negatively affect the growth of marine plants, then we have all the more reason to add large large quantities of this virus to waters to save the populations of shellfish that inhabit those waters.

Correct.


E. The amount of the virus naturally present in seawater in which brown tides occur is neither significantly greater nor significantly less than the amount present in seawater in which brown tides do not occur.

Irrelevant. Eliminate.