You use an independent samples t statistic when a. The IV defines two independent samples and the DV is measured on an interval/ratio scale
b. The IV defines two matched samples and the DV is measured on an interval/ratio scale.
c. The IV defines one sample, the DV is measured on an interval/ratio scale, and the DV is measured twice on that same sample.
d. The IV defines one sample and the DV is measured on an interval/ratio scale and you do not know the population standard deviation.
e. The IV defines one sample and the DV is measured on an interval/ratio scale and you do know the population standard deviation