Itis(was)被强调部分+that(who)+句子其他部分.

　　此结构强调的成分仅限于主语,宾语和状语.

　　Itisfromthesunthatwegetlightandheat.

　　ItwasnotuntilIhadreadyourletterthatIunderstoodthetruestateofaffairs.

　　典型例题

　　1）Itwaslastnight___Iseethecomet.

　　A.thetimeB.whenC.thatD.which

　　答案C.强调句的结构是：It+be+强调部分+that(who)+主谓句.强调句的连词只有两个,that和who.当强调的部分是人,且为句子的主语时,才用"who",其余用that.

　　原句：Myfatherdidtheexperimentinthelabyesterdayevening.

　　强调主语：Itwasmyfatherwhodidtheexperimentinthelabyesterdayevening.

　　强调宾语：Itwastheexperimentthatmyfatherdidinthelabyesterdayevening.

　　强调时间：Itwasyesterdayeveningthatmyfatherdidtheexperimentinthelab.(注意不用when)

　　强调地点：Itwasinthelabthatmyfatherdidtheexperimentyesterdayevening.

　　2）Itistenyears___MissGreenreturnedtoCanada.

　　A.thatB.whenC.sinceD.as

　　答案C.考点是连词用法.本题易误选为A.that.其实本句不是强调句.若是,去掉Itbe…that还应是一个完整的句子.而本句去掉'Itis…that',只剩下tenyearsMissGreenreturnedtoCanada.不成句.因此本句不是强调句.

　　Itis/was+时间+since…其中ishasbeenwashadbeen.