In 2016, engineer Vanessa Galvez oversaw the installation of 164 bioswales, vegetated channels designed to absorb and
divert stormwater, along the streets of Queens, New York. By reducing the runoff ﬂowing into city sewers, ______
the mitigation of both street ﬂooding and the resulting pollution of nearby waterways has been achieved by bioswales.
the bioswales have mitigated both street ﬂooding and the resulting pollution of nearby waterways.
the bioswales’ mitigation of both street ﬂooding and the resulting pollution of nearby waterways has been achieved.
both street ﬂooding and the resulting pollution of nearby waterways have been mitigated by bioswales.
Choice B is the best answer. The convention being tested is subject-modiﬁer placement. This choice makes the noun phrase
“the bioswales” the subject of the sentence and places it immediately after the modifying phrase “By reducing…sewers.” In
doing so, this choice clearly establishes that the bioswales—and not another noun in the sentence—are reducing runoff
ﬂowing into city sewers.
Choice A is incorrect because it results in a dangling modiﬁer. The placement of the noun phrase “the mitigation…
waterways” immediately after the modifying phrase results in unclear modiﬁcation. The resulting sentence makes it hard to
determine what is responsible for “reducing the runoff”: the bioswales or some other noun in the sentence. Choice C is
incorrect because it results in a dangling modiﬁer. The placement of the noun phrase “the bioswales’ mitigation…waterways”
 immediately after the modifying phrase results in unclear modiﬁcation. The resulting sentence makes it hard to determine
what is responsible for “reducing the runoff”: the bioswales or some other noun in the sentence. Choice D is incorrect
because it results in a dangling modiﬁer. The placement of the noun phrase “street ﬂooding and the resulting pollution”
immediately after the modifying phrase illogically suggests that the “ﬂooding and pollution” are reducing runoff ﬂowing into
city sewers.