The structure of the question is as follows
The rate of pickpocketing was increasing in Karlarinda's main airport -> airport authority posted big signs to warn people of such thefts and to beware of pickpockets -> after this, the rate of such theft increased.
The question asks to explain the paradox. The paradox is that after taking measures to control the theft, the theft increased. What can explain this.
A. Even if 40% people are unable to read signs, the remaining can. This should have resulted in a slight decrease, or worst case scenario, maintained the theft rates as the same levels as before the notice. This statement weakens the argument.
B. Karlarinda has been a shopping destination for 7 years while the change has been effective for only a year. This cannot explain the increase in the theft post sign installations as this cause was same before and after the change.
C. This is completely irrelevant. That one day of patrol does not explain anything.
E. If people took measures to safeguard their valuables after seeing the notices, this would have led to a reduction in theft rates. Hence this statement is a weakener or goes against explaining the paradox.
D. Best of the lot IMO. If after reading the notice, everyone immediately checks their valuables, any pickpocket nearby will immediately get to know where that person is keeping their valuables, thereby making it easier for the pickpocket to target the valuables. Not the best but best of the lot explanation.