Fill in the blanks.
In Hell-Volhard-Zelinsky reaction, the carboxylic acids are halogenated at ______ position by using _______ and ______.
A. `alpha`, NaOH, iodine
B. `alpha`, phosphorus, halogen
C. `beta`, phosphorus, `H_(2)O`
D. `beta, PCl_(5),NaOH`