Student’s t-test:– Paired Student’s t-test: Comparing means (± SD) in paired data (in same group of individuals before and after an intervention) – Unpaired Student’s t-test: Comparing means (± SD) in two different group of individuals – Z-test: Is a variant of student’s t-test which is used when sample size is > 30. In the given question, mean ± SD of 20 boys (140 ± 13 cm) and 20 girls (135 cm ± 7cm) of the same age are compared, Thus most appropriate statistical test of significance would be Unpaired Student’s t-test.