【简答题】已知等比数列{a n }中,a 6 ?a 7 =1,a 10 ?a 11 =16,则a 8 ?a 9 等于______.
【单选题】在正项等比数列{a n }中,a 1 ,a 19 分别是方程x 2 -10x+16=0的两根,则a 8 ·a 10 ·a 12 等于( )
【单选题】Mrs. Smith made her students _ the compositions three times a week.
【简答题】My classmates are busy ( ) (write) compositions.
【单选题】中国境内唯一合法承认跆拳道发证机构是哪?
【单选题】若代数式2a 2 +3a=1,那么代数式4a 2 +6a-10的值是( )
【简答题】Professor Wang had us (write) ______ compositions every Friday.