1. tito no es un niño muy sano. se enferma
2. el doctor garrido es muy puntual. siempre llega al consultorio
3. mi madre visita al doctor con frecuencia. se chequea una vez cada año.
4. fui al doctor el año pasado. tengo que volver
5. llegué tarde al autobús, que tengo que ir al centro caminando.
6. el examen fue difícil.

1) con frecuencia / a menudo

2) a tiempo

3) al menos  / por lo menos

4) pronto  / en breve

5) así  que

6) bastante

Explanation:

An adverb is a part of the sentence that complements a verb, an adjective, other adverbs and even sentences. Adverbs express circumstances, such as mode, place, time, quantity, affirmation, doubt, etc., answering questions such as when, where, how, how, among others. This function is called adverbial function, and can be carried out by isolated words (adverbs) or by groups of two or more words (adverbial phrases).

Some of the words considered by traditional pre-scientific grammar as adverbs can be considered in independent categories. For example, the adverbs of location, mode and quantity seem to form a natural class, but other adverbs ("epistemic", "adverbs of denial") seem to form a separate class from the syntactic point of view.