已知:x+y=4,x2﹣y2=20,则x﹣y的值是( ).
5
Look, she _____a book over there.
A .is reading B .is looking C .is seeing
(2013·高考福建卷)Not until he went through real hardship ________the love we have for our families is important.
A.had he realized
B.did he realize
C.he realized
D.he had realized