seriously (part of speech: adverb)
vigorously (part of speech: adverb)
excitedly, actively, fervently, powerfully, potently, passionately, ardently, lustily, spiritedly, animatedly, agitatedly, exuberantly, vigorously, enthusiastically, zealously, friskily, strongly, zestfully, emphatically, energetically, fierily, industriously
willingly (part of speech: adverb)
eagerly, pliably, adaptably, submissively, susceptibly, pliantly, cooperatively, persuadably, tractably, agreeably, flexibly, readily, tamely, compliantly, receptively, willingly, amenably, acquiescently, malleably
truthfully (part of speech: adverb)
- But don't say we shall never understand each other," she pleaded earnestly. - "Across the Zodiac", Percy Greg.
- Gravely, earnestly, his eyes searched her face and read her heart. - "The Doctor A Tale Of The Rockies", Ralph Connor.
- " Before you go I wish you would take this money," Teddy said, earnestly. - "The Adventures of a Country Boy at a Country Fair", James Otis.