Sentence Correction

GMATGuruNY wrote:

gmattoend wrote:In a study published by the US Fish and Wildlife Service, researchers proposed a cause for the chestnut die-off: a fungus called Cryphonectria parasitica, which was introduced to the United States in the early 1900s, invading the tree's bark, forms cankers as it spreads and lowering the pH of infected tissue to toxic levels, leads to the death of the tree within a short period.

A) invading the tree's bark, forms cankers as it spreads and lowering the pH of infected tissue to toxic levels, leads

B) invading the tree's bark, forming cankers as it spreads, lowering the pH of infected tissue to toxic levels, and leading

C) invades the tree's bark, forming cankers as it spreads and lowers the pH of infected tissue to toxic levels, leading

D) invades the tree's bark, forms cankers as it spreads and lowering the pH of infected tissue to toxic levels, leading

E) invades the tree's bark, forming cankers as it spreads and lowering the pH of infected tissue to toxic levels, leading

A conjunction such as and must serve to connect PARALLEL FORMS.
A and D: forms...and lowering
In these options, forms (verb) and lowering (modifier) are not parallel forms.
Eliminate A and D.

C: forming...and lowers
Here, forming (modifier) and lowers (verb) are not parallel forms.
Eliminate C.

In B, a fungus (subject) lacks a verb.
The result is an incomplete sentence.
Eliminate B.

The correct answer is E.

Generally, a COMMA + VERBing modifier serves to refer to the nearest preceding action and to the agent of that action.
E: A fungus invades the tree's bark, forming cankers as it spreads and lowering the pH of infected tissue to toxic levels, leading to the death of the tree within a short period.
Here, the COMMA + VERBing modifier in blue serves to refer to lowering (the nearest preceding action) and to a fungus (the agent of lowering), conveying that the COMMA + VERBing action (leading to the death of the tree) results from the action in red (lowering the pH to toxic levels).
Offhand, I cannot cite an OA from GMAC in which one VERBing modifier serves to refer to another VERBing modifier.

gmattoend wrote:Dear Mitch Sir,

In you previous posts, the VERBing modifier represents concurrent action. Do you see this happen in this sentence ? As per the sentence, 'leading to death ' happens in short period, So It is not concurrent action, sir? Can you explain please?