Final answer:
The correct word to complete the sentence is 'escribiendo' which means 'are writing'.
Step-by-step explanation:
The correct Spanish word to complete the sentence is escribiendo.
In Spanish, the word for 'are writing' is formed by combining the verb 'estar' (to be) with the present participle of the verb 'escribir' (to write). In this case, since the subject is plural (Amalia y Grisela), the correct form of the verb is 'están escribiendo'.
Example: Amalia y Grisela están escribiendo una canción hermosa.
Learn more about Spanish verb conjugation