**Core Concept**
The question is testing the student's knowledge of the chemistry of carbohydrates and its application in the treatment of deep vein thrombosis (DVT). The underlying principle is the role of heparin, an anticoagulant, in preventing clot enlargement by inhibiting the coagulation cascade.

**Why the Correct Answer is Right**
Heparin works by binding to antithrombin III, a naturally occurring anticoagulant protein, and enhancing its ability to inactivate thrombin and other coagulation enzymes. This leads to a decrease in the conversion of fibrinogen to fibrin, thereby preventing clot formation and enlargement. In the context of DVT, heparin is administered to prevent the clot from growing and breaking loose, which can lead to pulmonary embolism.

**Why Each Wrong Option is Incorrect**
* **Option A:** This option is incorrect because it does not mention a chemical that is commonly used to prevent clot enlargement in DVT. Other anticoagulants like warfarin or direct oral anticoagulants (DOACs) may be used, but they have different mechanisms of action and are not the first-line treatment.
* **Option B:** This option is incorrect because it is not a specific chemical or medication that is used to treat DVT. The treatment of DVT involves anticoagulation, but the specific chemical is not specified in this option.
* **Option D:** This option is incorrect because it is not a commonly used medication for the treatment of DVT. While aspirin may have some antiplatelet effects, it is not the primary treatment for preventing clot enlargement in DVT.

**Clinical Pearl / High-Yield Fact**
It's essential to remember that heparin is a highly charged, sulfated polysaccharide that is derived from the intestinal mucosa of pigs. It has a narrow therapeutic index, and its administration requires careful monitoring of the activated partial thromboplastin time (aPTT) to prevent bleeding complications.

**Correct Answer:** C. Heparin