Which are corrrect for choosing proppant A: for low permeability formations,the fracture mainly is requires to increases the length B: for low permeability formations,the fracture mainly is requires to increases fracture conductivity C: for medium or high permeability formations,the fracture mainly is requires to increases the length. D: for medium or high permeability formations,the fracture mainly is requires to increases fracture conductivity.

How many battle formations are there in Pit No. 2?

50. ___ A: They are newer than the formations in most caves. B: They were formed by sulfuric acid. C: They have been artificially preserved. D: They are smaller than those in any other cave.