understanding, comprehension / appreciation

seriousness

serious, deep, heavy (topic), profound (change), weighty (matter)

understand, comprehend / appreciate

question, problem on homework etc. / a question; a matter (of time etc.) / a problem (something that needs to be dealt with); a trouble / an issue; a matter

becoming more serious

become more serious

impossible to understand, utterly confused

unthinkable, out of the question

(informal) no problem