The commercial correspondence has changed over time and lost its bombastic and formal style, but nevertheless the … differs in some respects from the personal letter.

Collecting data through any of the methods may … some ethical issues in relation to the participants and the researcher.

The secondary literature… publications that rely on primary sources for information.

Those … who entered the Institute get an opportunity to major in almost all branches of mathematics as they are obligatory subjects in this specialization.

It is important to note that the form that a publication takes no guide to its classification as primary, secondary or … literature.