This is the 2679th most frequent German word.
ernsthaft
Serious or earnest.
In this sentence, 'ernsthaft' is used as an adverb describing how the subject takes the action of 'taking the question'—in a serious and sincere manner.
Ich nehme deine Frage ernsthaft, weil sie wichtig ist.
I take your question seriously because it is important.
Here, 'ernsthaft' is used as an adjective to describe the noun 'Schüler' (student), indicating that the student has a dedicated and committed attitude toward studying.
Er ist ein ernsthafter Schüler, der viel Zeit mit Lernen verbringt.
He is a serious student who spends a lot of time studying.
In this example, 'ernsthaft' functions as an adverb modifying the verb 'behaupten' (claim), emphasizing the seriousness or sincerity of the claim being made.