Which of the following are true about gypsum bonded casting investments?
1. should be allowed to set a minimum of 45 minutes
2. should be heated no longer than 30 minutes at 900 degrees F
3. the mold temperature should not exceed 1200 degrees F
4. used for alloys with melting temperatures exceeding 1800 degrees F
5. ideal mold temperature for hygroscopic technique is 875 degrees F
- 1, 2, 3, 5
- 1, 3, 5
- 2, 3, 4
- all of the above
- none of the above are correct statements
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