Which one of the following shows a unique relationship with an insect that has coevolved with it and that is the only insect that can pollinate this tree?

Answer: A. Fig has the unique coevolved relationship with a single insect pollinator. The fig (Ficus species) has one of the most famous mutualistic relationships in nature with the FIG WASP (family Agaonidae). Each fig species is typically pollinated by ONE specific wasp species. The wasp enters through the ostiole of the fig syconium, pollinates the female flowers and lays eggs inside. The fig fruit is biologically an inverted inflorescence and cannot be pollinated by any other insect. Distractors fail: Mahua is pollinated by bats and various insects (not species-specific). Sandalwood is pollinated by various bees, flies and beetles. Silk cotton (Bombax ceiba) is pollinated by birds (sunbirds, mynas) and bats. Source: NCERT Class 12 Biology Ch 1 (Reproduction in Organisms) + standard ecology references on plant-pollinator coevolution.