**Core Concept**
Platelets, also known as thrombocytes, are a component of blood whose function is to stop bleeding by cloting blood vessel injuries. They contain various organelles and granules that play a crucial role in the coagulation process. The **alpha-granules** and **dense granules** are two types of granules found in platelets.

**Why the Correct Answer is Right**
The correct answer is related to the content of platelet granules. Platelets contain **alpha-granules**, which store proteins such as **fibrinogen**, **von Willebrand factor**, and **platelet factor 4**. These proteins are essential for platelet adhesion and aggregation.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it does not accurately describe the contents of platelet granules.
**Option B:** This option is also incorrect as it is unrelated to the components of platelets.
**Option C:** This option is incorrect because it is not a known component of platelets.

**Clinical Pearl / High-Yield Fact**
It is essential to remember that platelet dysfunction can lead to bleeding disorders, such as **thrombocytopenia**. Understanding the components of platelets is crucial for diagnosing and managing these conditions.

**Correct Answer:** D. alpha-granules and dense granules