Final answer:
The correct indefinite article for the word 'lección' is 'A' when considering the pronunciation rules for English indefinite articles.
Step-by-step explanation:
The correct indefinite article for the Spanish word lección, which translates to "lesson" in English, is 'una'. However, as the options provided are in English, the best match would be "A" because "lección" starts with a consonant sound when pronounced in Spanish. In English, the indefinite articles 'a' and 'an' are used depending on the pronunciation of the word that follows them. 'A' is used before words that begin with a consonant sound, and 'an' is used before words that begin with a vowel sound.