Practice question

Go with B — Different sieve tubes carry flow in opposite directions. Under PHLOEM TRANSLOCATION, this is the standard explanation you’d use in class: it names the real driver or definition, while the rest are nearby but wrong. Not these: A) Phloem sap flows both ways in one sieve tube; C) Diffusion occurs freely; D) Xylem assists phloem. When two options sound similar, choose the one that matches the textbook definition most tightly.