Which of the following are the special features of a hermetically sealed compressor of a refrigerator?
1. The compressor may be reciprocating to rotary type
2. No shaft seal is necessary
3. More silent in operation
4. COP is more than that of open compressor
(a) 2 and 4 (b) 1,2 and 3 (c) 1, 3 and 4 (d) 2, 3 and 4