Researcher Lin Zhi developed a process for increasing the tensile strength—measured in gigapascals, or GPa—of silkworm
______ dissolving and reweaving the silk in a solution of iron metal ions, zinc, and sugar, Zhi increased the amount of force
required to stretch it from approximately 0.5 GPa to 2 GPa.
silk, by
silk by
silk and by
silk. By
Choice D is the best answer. The independent clauses "researcher Lin Zhi…silk" and "by dissolving…2 GPa" can be
grammatically separated by a period. They can stand alone as sentences, and this is the only choice that lets them do that.
Choice A is incorrect. This choice results in a grammar error called a comma splice. "Researcher Lin Zhi…silk" and "by
dissolving…2 GPa" are both independent clauses. They need to either be separated with punctuation like a period or a
semicolon, or they need to be connected by a comma and a coordinating conjunction like "and." A comma alone isn’t
enough. Choice B is incorrect. This choice results in a grammar error called a run-on sentence. "Researcher Lin Zhi…silk" and
"by dissolving…2 GPa" are both independent clauses. They need to either be separated with punctuation like a period or a
semicolon, or they need to be connected by a comma and a coordinating conjunction like "and." Choice C is incorrect. This
choice results in a grammar error called a run-on sentence. "Researcher Lin Zhi…silk" and "by dissolving…2 GPa" are both
independent clauses. The coordinating conjunction "and" isn’t enough to link them by itself. We need a comma, too.