**Core Concept**
The question is testing the understanding of post-translational modifications that regulate enzyme activity. Covalent phosphorylation is a key mechanism by which enzymes are activated or inhibited in various cellular pathways.

**Why the Correct Answer is Right**
Enzymes activated by covalent phosphorylation are typically protein kinases, which are enzymes that transfer phosphate groups from high-energy donors to protein substrates. This process involves the transfer of a phosphate group from ATP to the target enzyme, resulting in a conformational change that activates the enzyme. This mechanism is crucial in signal transduction pathways, where it allows for rapid and reversible regulation of enzyme activity.

**Why Each Wrong Option is Incorrect**
* **Option A:** This option is incorrect as it does not specify the type of enzyme that is activated by covalent phosphorylation. While some enzymes may be inhibited by phosphorylation, the question specifically asks for enzymes activated by this process.
* **Option B:** This option is incorrect as it refers to a different type of post-translational modification, where the enzyme is activated by the removal of a phosphate group. This process is also known as dephosphorylation.
* **Option C:** This option is incorrect as it is a type of enzyme that is actually inhibited by covalent phosphorylation. Protein phosphatases are enzymes that remove phosphate groups from protein substrates, resulting in the inhibition of enzyme activity.

**Clinical Pearl / High-Yield Fact**
Phosphorylation and dephosphorylation reactions are reversible and can be catalyzed by specific enzymes. Understanding these post-translational modifications is crucial in understanding the regulation of enzyme activity in various cellular pathways.

**Correct Answer: C. Protein phosphatases.