Answer: A, B
Pyridine supplies free chloride for the backside displacement, giving inversion, and the SN2 displacement of −OPBrX2 avoids carbocations. Neopentyl alcohol in concentrated acid either reacts extremely slowly or rearranges through a cation and does not give neopentyl chloride cleanly. Tosylation only breaks the O-H bond; the C-O bond is untouched, so the configuration is retained, not inverted.