(A) Portrait photographer London
(B) London photographer
(C) London portrait photographer
(D) Photographers in London
If a keyword is enclosed in square brackets like this one  then the search query has to be an exact match. This means the search query has to match exactly to the keyword in order to trigger an ad based on that keyword. So, the search query for [London portrait photographer] has to be London portrait photographer which is an exact match to the keyword.
This question is a part of the Google Digital Unlocked and Google Digital Garage Certification exams. You can find all the latest updated questions and answers to both exams on our website in the Google Digital Garage and Google Digital Unlocked pages.