**Core Concept**
Acid-susceptible penicillins are a class of beta-lactam antibiotics that are inactivated by gastric acid, making them less effective when administered orally. This characteristic limits their use to parenteral administration.

**Why the Correct Answer is Right**
The acid-susceptible nature of these penicillins is due to their chemical structure, which contains a beta-lactam ring that is prone to hydrolysis by gastric acid. This degradation leads to the formation of inactive metabolites, rendering the antibiotic ineffective. The primary example of an acid-susceptible penicillin is penicillin G (also known as benzylpenicillin), which is often administered intravenously or intramuscularly to bypass gastric inactivation.

**Why Each Wrong Option is Incorrect**
* **Option A:** This option is likely a distractor and does not specify a particular type of penicillin. Without more information, it's difficult to assess its accuracy.
* **Option B:** This option might refer to a different class of penicillins, such as acid-stable penicillins (e.g., amoxicillin, ampicillin), which can withstand gastric acid and are often administered orally.
* **Option C:** This option could be a distractor or a type of penicillin that is not typically classified as acid-susceptible. Without further context, it's challenging to evaluate its accuracy.

**Clinical Pearl / High-Yield Fact**
When administering penicillin G, it's essential to use a parenteral route to ensure adequate absorption and efficacy. Oral administration of acid-susceptible penicillins can lead to significant degradation and reduced therapeutic effects.

**Correct Answer: C. Penicillin G**