21.over the period from...to...the...remained level. 在...至...期间，...基本不变。
22.in the year between...and... 在...年到...期间...
23.in the 3 years spanning from 1995 through 1998... 1995年至1998三年里...
24.from then on/from this time onwards... 从那时起...
25.the number of...remained steady/stable from (month/year) to (month/year). ...月(年)至...月(年)...的数量基本不变。