About 5 million acres in the United States have been invaded by leafy

Hello sevenplusplus,

I would be glad to help you resolve your doubt.

Let's take a look at the original sentence:

About 5 million acres in the United [u]States have been invaded by leafy spurge, a herbaceous plant from Eurasia with milky sap that gives mouth sores to cattle, displacing grasses and other cattle food and rendering rangeland worthless.[/u]

(Blue = subject, Green = verb, Pink = comma + verb-ing modifiers)

Let's understand what the sentence intends to convey. The sentence states that in the US, some 5 million acres of land have been invaded leafy spurge. Describing the leafy spurge, the sentence states that it's a plant from Eurasia. It has milky sap that gives mouth sores to cattle. This leafy spurge displaces grasses and other cattle food and renders rangeland worthless.

However, the way this sentence is worded, it suggests that because leafy spurge gives mouth sores to cattle, it displaces grasses and other cattle food and has rendered rangeland worthless.

We get this illogical meaning from the sentence because of the incorrect usage of the comma + verb-ing modifiers* displacing and rendering.

The comma + verb-ing modifier must modify the preceding action logically and must also make sense with the doer of the modified action.

In this official sentence, the comma + verb-ing modifiers displacing and rendering illogically modifies the preceding action gives by presenting the result of this action. Grasses and other cattle food are not displaced and rangeland are not rendered worthless because leafy spurge gives mouth sores to cattle.

This is the reason why Choice A is incorrect.

From the context of the sentence, we can understand that because leafy spurge displaces grasses and other cattle food, rangeland are rendered useless. So we do have this logical cause-and-effect in the sentence that must be communicated in correct grammar.

Let's evaluate Choice B now:

About 5 million acres in the United States have been invaded by leafy spurge, a herbaceous plant from Eurasia, with milky sap, that gives mouth sores to cattle and displaces grasses and other cattle food, rendering rangeland worthless.

This choice correctly conveys the logical intended meaning. The comma + verb-ing modifier displacing has been turned to simple present tense verb displaces. The comma + verb-ing modifier rendering correctly modifies the preceding action displaces, presenting the result of this action. Because the leafy spurge displaces grasses and other cattle food, it renders rangeland worthless.

*The correct usage of comma + verb-ing has been covered in great details and with pertinent examples in our SC course, In fact, this concept features in the Free Trail course offered by e-GMAT. You can register for free at e-gmat.com and review the concept.


Hope this helps.
Thanks.
Shraddha