Water Flows into the Source End of a Sieve Tube

Water flows into the source end of a sieve tube because

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