21-important

　　• substantial

　　• weighty (important and serious)

　　• weighty issues/matters

　　• notable

　　22-interesting

　　• absorbing

　　• appealing

　　• thought-provoking

　　23-job

　　• undertaking

　　• The construction of the tunnel is a large and complex undertaking.

　　• occupation

　　• vocation

　　24-know

　　• comprehend

　　• perceive

　　• discern

　　25-like (v.)

　　• enjoy

　　• relish

　　• appreciate

　　• have a predilection for

　　26-main

　　• primary

　　• foremost

　　• dominant

　　27-more

　　• supplementary

　　• additional

　　• replenishment

　　28-next

　　• subsequently

　　• thereafter

　　• successively

　　29-nice

　　• gracious

　　• charming

　　• satisfying

　　30-really

　　• genuinely

　　• undeniably

　　• truly