— Yes. He never praised him ________ he became one of the top students in his grade.
A:after
B:unless
C:if
D:when
读德国相关图文材料,回答下列问题
发展乳畜业需要大量的多汁牧草(生长过程喜湿喜温).经济高度发达的德国位于欧洲中部,北部濒临北海、波罗的海.该国乳畜业十分发达,乳畜产品大量出口.
已知,a→=(2,1),a→·b→=10,a→+b→=52,则b→=( )