hard
This stone is very hard.
strong
This box is very sturdy.
solid
This box is very sturdy.
sure
You are indeed intelligent, but you still cannot be arrogant.
assuredly
He is certainly intelligent, but he doesn't work hard.
undoubtedly
He is certainly intelligent, but he doesn't work hard enough.
of course
This is certainly good, but it is still not enough.
indeed
He is certainly intelligent, but he does not work hard.
admittedly
Although he worked very hard, the results were not ideal.
hard
This stone is very hard.
strong
This box is very sturdy.
solid
This box is very sturdy.
sure
You are indeed intelligent, but you still cannot be arrogant.
assuredly
He is certainly intelligent, but he doesn't work hard.
undoubtedly
He is certainly intelligent, but he doesn't work hard enough.
of course
This is certainly good, but it is still not enough.
indeed
He is certainly intelligent, but he does not work hard.
admittedly
Although he worked very hard, the results were not ideal.