## **Core Concept**
The question tests understanding of the secretion and activation of digestive enzymes in the gastrointestinal tract. Many digestive enzymes are secreted in an inactive form called **zymogens** or **proenzymes**, which are then activated in the intestine to prevent autodigestion of the pancreas and other tissues.

## **Why the Correct Answer is Right**
Pepsinogen is the zymogen form of **pepsin**, a gastric enzyme. Trypsinogen, chymotrypsinogen, and procarboxypeptidase are zymogens of pancreatic enzymes. **Gastric amylase** is secreted in an active form from the salivary glands and gastric mucosa, not as a zymogen. Therefore, gastric amylase does not require activation in the same way that pancreatic and gastric digestive enzymes do.

## **Why Each Wrong Option is Incorrect**
* **Option A:** Pepsinogen is indeed secreted as a zymogen. It is activated to pepsin in the stomach by hydrochloric acid.
* **Option B:** Trypsinogen is a zymogen secreted by the pancreas. It is activated to trypsin in the intestine by enterokinase.
* **Option C:** Chymotrypsinogen is also a zymogen secreted by the pancreas. It is activated to chymotrypsin.
* **Option D:** This option does not need evaluation as it corresponds to the correct answer.

## **Clinical Pearl / High-Yield Fact**
A key point to remember is that the activation of zymogens into their active enzyme forms is crucial for digestion and is tightly regulated to prevent inappropriate activation within the pancreas or stomach, which could lead to damage or disease, such as **pancreatitis**.

## **Correct Answer: D. Gastric amylase**