Water Flows into the Source End of a Sieve Tube

Multiple Choice

Water flows into the source end of a sieve tube because ________.

A) sucrose has been actively transported into the sieve tube, making it hypertonic
B) water pressure outside the sieve tube forces in water
C) the companion cell of a sieve tube actively pumps in water
D) sucrose has been transported out of the sieve tube by active transport