Which two statemets 

Which two statemets are true？（）

• ADPT/RPR uses a bi-directional ring consisting of two symmetric counter rotating fibre rings.
• BDPT/RPR is defined in the IEEE 802.17 standard and it uses Token Bucket system to avoid collisions on the fiber.
• CIn DPT/RPR rings， data packets can be sent in one direction （downstream） and the corresponding control packets in the opposite direction （upstream），thus using both fibres concurrently to maximise bandwidth.
• DDPT/RPR can be deployed in the Core of the SP networks where point-to-point POS links are used tomake best use of the Bandwidth.