QUES: Under questioning from journalists Turnbull gave his definition of a backdoor

correct the punctuation.

CORRECTED: Under questioning from journalists, Turnbull gave his definition of a backdoor.

QUES: The same is true for subtitles and you may combine the two as well if you want

correct the punctuation.

CORRECTED: The same is true for subtitles, and you may combine the two as well if you want.

QUES: She gave an invited address to the International Congress of Mathematicians in Zrich in 1994

correct the punctuation.

CORRECTED:
She gave an invited address to the International Congress of Mathematicians in Zurich in 1994.