An old man lived in the village. He was one of the (1) ______ unfortunate people in the world. The whole village was tired (2) ______ him; he was always gloomy, he (3) ______ complained and was always in a bad mood. The (4) ______ he lived, the more vile he was becoming and the more (5) ______ were his words.

Select the most appropriate option to fill in blank number 3.

To determine the most appropriate word to fill in blank (3), let us analyze the context of the sentence:
"The whole village was tired (2) ______ him; he was always gloomy, he (3) ______ complained and was always in a bad mood."

The sentence describes the old man's persistent and habitual negative behavior. The key clues are the words "always gloomy" and "always in a bad mood". This indicates that his complaining was not occasional, cyclic, or done in a general/common manner, but rather occurred continuously without stopping.

Let us evaluate the given options:
1. mostly: Means "for the most part" or "mainly". While he complained often, "mostly" does not capture the continuous, unceasing nature of his actions implied by "always".
2. commonly: Means "usually" or "frequently". This describes how typical the action is, but lacks the emphasis on continuous repetition in time.
3. cyclically: Means "occurring in cycles" or "periodically". Complaining in cycles does not match the description of someone who is "always" gloomy and in a bad mood.
4. constantly: Means "continuously", "over a period of time", or "always". This perfectly matches "always gloomy" and "always in a bad mood", showing that his complaining was continuous and habitual.

Therefore, the correct word to fill in blank (3) is constantly.