QUES: He spent a year abroad then in 1903 he returned to become a professor at Moscow University

correct the punctuation.

CORRECTED: He spent a year abroad, then in 1903 he returned to become a professor at Moscow University.

QUES: A maximum of 200 hours of overtime per year is allowable or 300 hours under special agreements with the trade union

correct the punctuation.

CORRECTED: A maximum of 200 hours of overtime per year is allowable, or 300 hours under special agreements with the trade union.

QUES: Areas are todays zones and also there is an important and valuable limitation that use is regulated by the authorities

correct the punctuation.

CORRECTED:
Areas are today's zones and also there is an important and valuable limitation that use is regulated by the authorities.