Movement into and out of cells — practice question

Which row gives the cause of mass flow in the phloem and the direction in which phloem sap moves by mass flow?

• Acause: hydrostatic pressure gradient; direction: sink to source
• Bcause: hydrostatic pressure gradient; direction: source to sink
• Ccause: water potential gradient; direction: sink to source
• Dcause: water potential gradient; direction: source to sink