Answer:
statement 4
Explanation:
When Semyonov was called back to Moscow in 1944, his duties were assumed by his protégé, Alexander Feklisov. Feklisov cultivated a warm relationship with Julius, and eventually persuaded him to bring in his brother-in-law, David Greenglass — a machinist on the Manhattan Project — to supply the pipeline with information. Owing to the viewpoint that the U.S. should not possess the only atomic bomb, Julius managed to recruit Joel Barr, Al Sarrant, William Perl, and Morton Sobell.
Following the war, the U.S. was ultra-sensitive about sharing information with the U.S.S.R., so it came as a great surprise that the Soviets had managed to produce their own nuclear warhead. It was determined that German defector Klaus Fuchs, a theoretical physicist working for Great Britain, had passed secret documents to the Soviets via a courier.