En kies domo vi loĝas? In whose house do you reside?
Kies amikojn vi vizitis? Whose friends did you visit?
THE PRESENT ACTIVE PARTICIPLE.
108. A participle is a verbal adjective, as in "a crying child." It agrees like other adjectives with the word modified (19, 24). The participle from a transitive verb (22) may take a direct object, and a participle expressing motion may be followed by an accusative indicating direction of motion (46). The present active participle, expressing what the word modified is doing, ends in -anta, as vidanta, seeing, iranta, going:
La ploranta infano volas dormi, the crying child wishes to sleep.
Mi vidas la falantajn foliojn, I see the falling leaves.
Kiu estas la virino aĉetanta ovojn? Who is the woman buying eggs?
Mi parolis al la viroj irantaj vilaĝon, I talked to the men (who were) going toward the village.
COMPOUND TENSES.
109. A participle may be used predicatively with a form of esti, as Mi estas demandanta, I am asking, La viro estas aĉetanta, the man is buying. Such combinations are called compound tenses, in contrast to the simple or aoristic tenses.
An aoristic tense consists of but one word (ending in -as, -os, etc.) and expresses an act or state as a whole, without specifying whether it is finished, still in progress, or yet begun.
Compound tenses occur less often in Esperanto than in English, and an aoristic Esperanto tense may often be translated by an English compound tense, as La birdoj flugas, the birds are flying. When used to form a compound tense, the verb esti is called the auxiliary verb. No other verb is ever used as an auxiliary (a simpler method than in English, which uses be, have, do, will, shall, would, etc.).
THE PROGRESSIVE PRESENT TENSE.
110. The compound tense formed by using the present active participle with the present tense of esti is called the progressive present tense. It differs from the aoristic present by expressing an action as definitely in progress, or a condition as continuously existing, at the moment of speaking. The conjugation of vidi in this tense is as follows: