**Core Concept**
Mycoplasmas are a unique group of bacteria that lack a cell wall and have a small genome, making them resistant to many antibiotics that target cell wall synthesis. They are capable of multiplying by binary fission and can grow in cell-free media, but their cell membrane structure and lack of a cell wall make them resistant to certain classes of antibiotics.

**Why the Correct Answer is Right**
Mycoplasmas are inherently resistant to beta-lactam antibiotics, such as penicillins and cephalosporins, due to their lack of a cell wall. These antibiotics work by inhibiting cell wall synthesis, but mycoplasmas do not have a cell wall to begin with, making them resistant to these drugs. In contrast, mycoplasmas are often sensitive to macrolides, tetracyclines, and other antibiotics that target protein synthesis or other cellular processes.

**Why Each Wrong Option is Incorrect**
**Option A:** Mycoplasmas do multiply by binary fission, which is a characteristic of bacteria. This statement is true and is not the correct answer.
**Option C:** Mycoplasmas can indeed grow in cell-free media, which is a unique characteristic of these bacteria. This statement is also true and is not the correct answer.
**Option D:** Mycoplasmas do require sterols for their growth, which is a critical component of their cell membrane. This statement is true and is not the correct answer.

**Clinical Pearl / High-Yield Fact**
Mycoplasmas are often resistant to beta-lactam antibiotics, but they can be treated with macrolides, tetracyclines, or other antibiotics that target protein synthesis. It's essential to consider the unique characteristics of mycoplasmas when selecting an antibiotic for treatment.

**✓ Correct Answer: B. Are sensitive to beta-lactam group of drugs.**