Teacher: Given the following Catalan sentence, indicate the name entities (i.e., the real-world objects such as a person, location, organization, etc. that can be denoted with a proper name) such as 'New York Times'.  For each words of a named-entity, indicate their type 'LOC' or 'ORG' or 'PER', where 'LOC' indicates a location entity (such as 'New York City', 'ORG' indicates the token of an organization (such as 'Amazon'), 'PER' indicates the tokens of a person entity (such as 'Jeff Bezos'). Named entities with other types should be indicated with 'MISC'. To indicate boundaries of an entity, use IOB (Inside-Output-Begin) prefixes. The B- prefix before a tag indicates that the word is the beginning of a named entity. The I- prefix indicates that the word is inside a bigger chunk. For example, you can break 'New York' to 'New' and 'York.' and tag them as 'B-LOC' and 'I-LOC'. Any token that doesn't belong to a named entity must be tagged with 'O'. 
Teacher: Now, understand the problem? If you are still confused, see the following example:
Una setantena de treballadors de Fomento de Construcciones y Contratas a Manresa , gairebé la totalitat de la plantilla , s' han manifestat aquest migdia pels carrers de la ciutat .
Solution: Una (O) setantena (O) de (O) treballadors (O) de (O) Fomento (B-ORG) de (I-ORG) Construcciones (I-ORG) y (I-ORG) Contratas (I-ORG) a (O) Manresa (B-LOC) , (O) gairebé (O) la (O) totalitat (O) de (O) la (O) plantilla (O) , (O) s' (O) han (O) manifestat (O) aquest (O) migdia (O) pels (O) carrers (O) de (O) la (O) ciutat (O) . (O)
Reason: We split the sentence into single words or punctuation and then assigned correct tags to each token as per the definition. We assigned 30 correct tags to the given sentence.

Now, solve this instance: Els dos trens que s' han vist afectats han estat el regional Lleida-Barcelona , que ha patit un retard de 20 minuts , i el regional Barcelona-Lleida , amb un retard de dues hores .
Student:
Els (O) dos (O) trens (O) que (O) s' (O) han (O) vist (O) afectats (O) han (O) estat (O) el (O) regional (O) Lleida-Barcelona (B-LOC) , (O) que (O) ha (O) patit (O) un (O) retard (O) de (O) 20 (O) minuts (O) , (O) i (O) el (O) regional (O) Barcelona-Lleida (B-LOC) , (O) amb (O) un (O) retard (O) de (O) dues (O) hores (O) . (O)