In the early 1970's, when art reached its current high levels of popularity and value, a rash of thefts of works by great artists occurred in major art museums around the world.
Basically a lot of pieces of art were stolen from the museums around the globe
But, after 1975, sophisticated new security systems were installed in every major museum. As a consequence, important thefts in major museums declined markedly.
Then the same museums put in place sophisticated alarm systems so the party was over
pretty straight argument. We have to find reasoning that reinforce this. A case, basically
(A) The typical art work stolen during both the 1970's and the 1980's was a small piece that could be concealed on the person of the thief.
The kind of art stolen if the painting was from caravaggio or dali or big or small nothing says us
(B) Premiums paid by major museums to insure their most important works of art increased considerably between 1975 and 1985.
The premium insurance paid for is irrelevant for our case
(C) The prices paid to art thieves for stolen works were lower during the 1980's than the prices paid to art thieves for comparable works during the 1970's.
The price that someone paid for to obtain the piece of art does not help us
(D) Thefts from private collections and smaller galleries of works by great artists increased sharply starting in the late 1970's.
Bingo. The number of thefts in private galleries went up and those from the museums went down. The alarm systems worked out. Bingo
(E) Art thefts in Europe, which has the largest number of works by great artists, outnumbered art thefts in the United States during the 1980's.
The comparison Europe vs US is irrelevant
Hope this helps