Final answer:
The correct form of the verb is 'hablando'.
Step-by-step explanation:
The correct form of the verb to complete the sentence is hablando.
When using the verb estar to indicate an ongoing action, we conjugate it in the present participle form by adding -ando to the stem of -ar verbs, and -iendo to the stem of -er and -ir verbs.
For example, in this sentence, the stem of the verb hablar is habl and when we add -ando, we get hablando.
Learn more about Spanish verb conjugation