The purpose of stratified random sampling is to make certain of

Stratified random sampling aims to secure proportionate representation from the different categories.

Studying only the largest group would ignore smaller strata and distort the picture.

A prompt response from respondents concerns fieldwork speed, not the aim of stratification.

Stratified sampling still requires randomization within each stratum, so no-randomization is wrong.

Dividing into strata reduces sampling error by controlling a known source of variation.

Proportionate allocation sets each stratum's sample in step with its share of the population.