Answer:
C. Folke Cronholm was secretly working for the Germans.
Step-by-step explanation:
B and D do not make any sense.
Folke Cornholm was very sketchy, and the reader can't infer that Folke Cronholm was spying for the Allied nations. It is C because he had made more visits than one would expect from a representative of the Swedish government. This is correct on E2020.