This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: general microbiology, Subject name: Microbiology
Which of the following is a feature of the cell envelope of Gram-negative bacteria? 
Select and explain. 
A. Teichoic acid present, B. Lipopolysaccharide Present, C. Porin proteins are absent, D. Periplasm absent
B: Lipopolysaccharide Present
Answer: B: Lipopolysaccharide Present 
Explanation: FeaturesGram-PositiveGram-NegativePeptidoglycanThick layerThin layerTeichoic acidsPresentAbsentOuter membraneAbsentPresentLipopolysaccharide(endotoxin)AbsentPresentPorin proteinsAbsentPresent; allow passage ofmolecules through the outer membranePeriplasmAbsentPresentRef: Jawetz Medical Microbiology; 27th edition; Page no: 23