What is the plot of the 1937 film 'Thank You, Mr. Moto' about?

A. Mr. Moto battles treasure hunters for ancient scrolls revealing the location of Genghis Khan's tomb
B. Mr. Moto investigates a murder in a small American town
C. Mr. Moto solves a mystery involving a stolen artifact
D. Mr. Moto goes undercover to stop a group of smugglers
Answer: 