Answer: 4.
This is a free search engine maintained by the United States National Library of Medicine.
It is used for accessimg and searching of MEDILINE database.
Medline is an acronym for (Medical Literature Analysis and Retrieval System Online) it is conprehensive bibilography of research materials in fields of biomedicine and life sciences.It contains abstracts and references of related journals.
It is an online repository for biomedical research materials
It also helps to promotes the concept of evidence based medicine.(The concept of clincal medicine that depends on the combination of available research evidences with patients values and clincal research.)
Therefore the use of Pubmed is to gain access into all the information above in the MEDLINE.