What Component of an HPLC Introduces an Aliquot of Sample

Multiple Choice

What component of an HPLC introduces an aliquot of sample into the column and how is this introduction accomplished with the high pressure in the flow path?

A) A syringe is used with a flexible tip placed into the flow path.
B) A flame ionizes the sample and sprays it into the column.
C) A flexible septum is coated with sample and placed in the column.
D) A fixed-loop injector with a switching valve moves the sample into the flow path.