Use the Following Paragraph to Answer the Corresponding Question

Use the following paragraph to answer the corresponding question.
Masatomo Kawakubo et al. reported in Science in August 2004 that the human stomach contains a natural, carbohydrate-based antibiotic that probably protects a large portion of the population from various diseases caused by the bacterium Helicobacter pylori. This bacterium has been linked to peptic ulcers, gastritis, and stomach cancer. This naturally occurring antibiotic is described by Kawakubo as having a terminal α-1,4-linked N-acetylglucosamine (NAG) , and it acts by inhibiting the biosynthesis of a major component of the cell wall in H. pylori. [SOURCE: M. Kawakubo et al., Science 305 (2004) : 1003.]
Refer to the paragraph about Kawakubo's group. Kawakubo's group created a glycoprotein with a terminal NAG (i.e., a protein with NAG attached to its end) . Their hypothesis is that the terminal NAG, and not the protein component, is responsible for the damage to the cell wall in H. pylori. What would be the most appropriate control for testing this hypothesis?

A) Grow H. pylori in a test tube (in vitro) with no glycoprotein.
B) Destroy the H. pylori by exposing them to a hypotonic solution. Then add the glycoprotein and observe.
C) Expose other species of bacteria to the glycoprotein.
D) Grow H. pylori in a test tube with a glycoprotein that has its terminal NAG removed.