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