This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: General, Subject name: Microbiology
True about sex pilus 
Select and explain. 
A. Hollow tubular structure binding bacteria during conjugation, B. During conjugation host DNA is always transferred, C. Plasmid is transferred always, D. ?
A: Hollow tubular structure binding bacteria during conjugation
Answer: A: Hollow tubular structure binding bacteria during conjugation 
Explanation: Ans: a) (Hollow tubular....) Ref: Medical microbiology Jawetz 23nl ed. Baily & Scott's diagnostic microbiology 12th edCONJUGATION* Process where male/ donor bacterium mates or makes physical contact with female/ recipient bacterium & transfers genetic elements into it. 1st described by Lederberg & Tatum in E coli called K12.* Plasmids are the genetic elements most frequently transferred by conjugation. But hostDNA& transposons all can be transferred by conjugation.* Fertility factor carried on plasmid is designated F+. This plasmid confers certain donor characteristics upon cells; these characteristics include a sex pilus: an extracellular multimeric protein extrusion that attaches donor cells to recipient organism lacking F factor.* Plasmid DNA in donor replicates & a copy of it passes from door to recipient along sex pilus. Thus recipient becomes F+& can conjugate with other cells.* Along with plasmid DNA, a portion of host DNA is sometimes transferred.* When F exists in some cells in intergrated state with host chromosome - HFr