Which one is the proper word to begin this phrase: grande como?

The correct answer is: c. leí.

Yo leí el libro en 30 minutos.

Explanation:

This sentence means: I read the book in 30 minutes.

The verb to read is leer in Spanish.

As this example refers to a past and finished action, we use past tense.

Let's see the past tense conjugation for the verb leer:

1. yo leí                          1. nosotros/as leímos

2. tú leíste                     2. vosotros/as leísteis

3. él/ella leyó                3. ellos/as leyeron

Here, the duration of 30 minutes implies that the action took half an hour - it is finished.