Yo recomiendo que ellos la casa pronto.
a. limpian b. limpien

This sentence is given in the subjunctive mood. We know this because it uses que as a relative pronoun. We use the subjunctive to express desires, doubts, the unknown, the abstract, and emotions. So limpien is the conjugation of the verb limpiar for the third person plural in the subjunctive mood. Finally:

Yo recomiendo que ellos limpien la casa pronto

cuando era un niño durante el verano salía a jugar con mis mejores amigos, ¿verdad?

hi

choose the best informal 'tú' translation of the following sentence = run

it's an imperative form ===> corre (tú)

correr (présent)

corro

corres

corre

corremos

corréis

corren

none of thes are

imperative tense

corre (tú) > correct

corra (él/ella/ud)

corramos (nosotros)

corred (vosotros)

corran (ellos/ellas/uds)

hope this will : )