单选题 Classified by different aims, there are at least 4 major types of test, among which _______ is to discover what the testee already knows about the target language.

【正确答案】 B
【答案解析】[详细解答] A．素质测试是衡量学习者语言习得的资质，C. 成绩测试是对学习者某一阶段的某项课程掌握程度的测试，D．诊断性测试针对的是学习者对该语言的不知程度。故只有C．水平测试检测的是学习者对目标语言的已掌握程度。