In such a solvent containing at least a hydrocarbon, the ratio of the alcohol (particularly methanol or the like) to other solvents (for example, an ester such as ethyl acetate, and ethers such as tetrahydrofuran) is approximately, for example, the former/the latter (volume ratio, at 25??? C.)=from 10/90 to 99/1, preferably the former/the latter (volume ratio, at 25??? C.)=from 30/70 to 98/2, more