Questions for this exercise need to have the key variable set if the key signature is anything else than ''c'' major (or ''a'' minor). Example:

header {
  module = singchord
  version = "3.1.4"
  title = "Simple chords"
}
question { music = satb("c''|e'|g|c") }
question { music = satb("a'|e'|c'|a") }
question { key="d \major" music = satb("a'|fis'|d'|d") }
question { key="f \minor" music = satb("as'|f'|c'|f") }

See also “Cantar acorde”.