In comparison with PE,__ is or are correct（）
A. Nylon has a higher degree of crystallinity, and a higher melting point
B. Nylon has a higher degree of crystallinity, and a lower melting point
C. PVC and PAN have higher degrees of crystallinity, and higher melting points
D. PVC and PAN have lower degrees of crystallinity, and lower melting points
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Most polymers are flammable in their pure form, except___（）
A. Polystyrene
B. Poly（vinyl chloride）
C. Polytetrafluoroethylene
D. Polyimide
Natural rubber is a kind of（）
A. Thermoplastic polymers
B. Thermosetting polymers
C. Unsaturated polymers
D. Saturated polymers
The fundamental reactions involved in addition polymerization are ______（）
Addition to double bond and generation of a primary radical
B. Decomposition of initiator and transfer to initiator radicals
C. Initiation, propagation, transfer and termination
D. Initiation, propagation and termination
Usually，polymerization includes_, based on the mechanism involved in forming polymers（）
A. Chain growth polymerization
B. Condensation polymerization
C. Addition polymerization
D. Step growth polymerization
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