How many {mother} are for {Eros} ?
Which is the number of mothers that Eros had?
How many mothers did Eros have?
SELECT ( COUNT ( ?s ) AS ?a ) { resource:Eros property:mother ?s }
SELECT (COUNT(?obj) AS ?objs ) {
?statement <http://www.w3.org/1999/02/22-rdf-syntax-ns#subject> <http://wikidata.dbpedia.org/resource/Q121973> .
?statement <http://www.w3.org/1999/02/22-rdf-syntax-ns#predicate> <http://www.wikidata.org/entity/P25> .
?statement <http://www.w3.org/1999/02/22-rdf-syntax-ns#object> ?obj .
} 

SELECT (COUNT(?obj) AS ?value ) { wd:Q121973 wdt:P25 ?obj }
5