SB 2.8.17

yugāni yuga-mānaṁ ca
 dharmo yaś ca yuge yuge
avatārānucaritaṁ
 yad āścaryatamaṁ hareḥ
Word for word: 
yugāni — the different ages; yuga-mānam — the duration of each age; ca — as well as; dharmaḥ — the particular occupational duty; yaḥ ca — and which; yuge yuge — in each and every yuga, or particular age; avatāra — the incarnation; anucaritam — and the activities of the incarnation; yat — which; āścaryatamam — the most wonderful activities; hareḥ — of the Supreme Lord.
Translation: 
Please explain all the different ages in the duration of the creation, and also the duration of such ages. Also tell me about the different activities of the different incarnations of the Lord in different ages.
Purport: 

Lord Kṛṣṇa is the original Personality of Godhead, and all the incarnations of the Supreme Lord, although nondifferent from Him, are emanations from the Supreme. Mahārāja Parīkṣit inquired from the great and learned sage Śukadeva Gosvāmī about the different activities of such incarnations so that the incarnation of the Lord might be confirmed by His activities in the authoritative scriptures. Mahārāja Parīkṣit was not to be carried away by the sentiments of the common man to accept an incarnation of the Lord very cheaply. Instead he wished to accept the incarnation of the Lord by symptoms mentioned in the Vedic literatures and confirmed by an ācārya like Śukadeva Gosvāmī. The Lord descends by His internal energy without any obligation to the laws of material nature, and thus His activities are also uncommon. The specific activities of the Lord are mentioned, and one should know that the activities of the Lord and the Lord Himself are identical due to being on the absolute plane. Thus to hear the activities of the Lord means to associate with the Lord directly, and association with the Lord directly means purification from material contamination. We have already discussed this point in the previous volume.