Given the sample is small, the t-test is applied to conduct hypothesis test when
　　A.        the population sampled is normally distributed with known variance
　　B.        the population sampled is normally distributed with unknown variance
　　C.        neither A nor B, because t-test is only suitable for large sample
　　Solution: B
　　If the population sampled has unknown variance and either of the conditions below holds:
　　1 the sample is large, or
　　2 the sample is small but the population sampled is normally distributed, or approximately normally distributed,
　　then the test statistic for hypothesis tests concerning a single population mean, is