Given a context passage, generate a question from the passage such that its answer is shortest continous span from the passage.

Example Input: The President of the European Parliament (Parliament's speaker) is Martin Schulz (S&D), elected in January 2012.
Example Output: Who led European Parliament?

Example Input: While Clostridium difficile epidemiology is well documented in many European countries, data are largely missing for South Eastern European region. Here we report the PCR ribotype distribution of 249 C.difficile isolates received for typing from six hospital settings from Croatia, Bosnia and Herzegovina, Republic of Macedonia and Serbia in time period from 2008 to 2015. Twenty-four PCR ribotypes were detected. The majority of strains from Bosnia and Herzegovina and Serbia belonged to PCR ribotype 027 (65.8%). Other three dominating PCR ribotypes were 176 (18 strains; Croatia), 001/072 (15 strains; all countries) and 014/020 (15 strains; all countries).
Example Output: Which main ribotype of Clostridium difficile is responsible of the recent outbreak?

Example Input: Exosomes are a subset of extracellular vesicles (EVs) that have important roles in intercellular communication. They contain and carry bioactive molecules within their membranes which are delivered to target cells. Reproducible isolation and enrichment of these exosomes will aid in evaluation of cellular communication. We present an approach that involved the pre-processing of plasma, combined with ultracentrifugation (UC) and size exclusion chromatography (SEC) to isolate EVs and subsequently enrich exosomes. Four variations of this approach (denoted methods I to IV) were compared. Coupling an ultracentrifugation method with size exclusion chromatography (Method II) provided the best yield by nanoparticle tracking analyses (NTA), the presence of the exosomal markers CD63, Flotillin-1 and TSG-101 (immunoblotting) and showed exosome morphology using transmission electron microscopy (TEM). This method provides an efficient way to enrich the exosomes from blood (plasma), which could be potentially employed for clinical diagnostic assessment and therapeutic intervention.
Example Output:
What is an exosome?