10. According to the pressure-flow hypothesis, what is the driving force for the long-distance transport of phloem sap?
(A) Negative pressure (tension) generated by leaf transpiration.
(B) Active transport of sucrose into the sieve tube at the source, which lowers water potential and causes water uptake, generating local positive pressure.
(C) Active water pumping at the sink, creating a massive capillary action.
(D) High-speed cytoplasmic streaming driven by ATP within the sieve tube cells.

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