Which of the following descriptions are correct? (Multiple choice)

Which of the following descriptions are correct? (Multiple choice)
A . The difference between a 1+1 linear multiplex section and a 1:1 linear multiplex section is whether APS is required.
B. The 1:1 linear multiplex section can be equipped with additional services, and its switching mode is only double-ended recovery switching.
C. Whether it is a two-fiber bidirectional MSP ring protection ring or a four-fiber bidirectional MSP ring, there are requirements for the nodes in the ring. The main reason is that it is determined by the K1 and K2 bytes in the APS protocol.
D. The APS protocol of the four-fiber bidirectional multiplex section protection ring is carried by the protection optical fiber.
E. The protection mode of SNCP protection is " double transmission, selective reception", which is especially suitable for decentralized services.

Answer: BCD