Step 1: Match Plants to Characteristics:
I. Mustard (Brassicaceae):
Placentation: Parietal (False septum/Replum forms). Matches W.
Corolla: Valvate or Imbricate (often generalized as Valvate in matching questions relative to others). Matches D.
Pair: I - D - W.
II. Pea (Fabaceae):
Aestivation: Vexillary (Papilionaceous). Matches C.
Placentation: Marginal. Matches Z.
Pair: II - C - Z.
III. China Rose (Malvaceae):
Aestivation: Twisted. Matches B.
Placentation: Axile. Matches Y.
Pair: III - B - Y.
IV. Sunflower (Asteraceae):
Flower Type: Disc florets have Tubular corolla. Matches A.
Placentation: Basal. Matches X.
Pair: IV - A - X.
Step 2: Verification:
The sequence is:
I-D-W, II-C-Z, III-B-Y, IV-A-X.
This matches Option (B).