Consider the following:1.Birds2.Dust blowing3.Rain4.Wind blowingWhich of the above spread plant diseases?

1. A

   1 and 3 only

   (a) 1 and 3 only. Birds and rain do spread pathogens and spores, but dust and wind are equally classic dispersal agents. This option is not the key.

2. B

   3 and 4 only

   (b) 3 and 4 only. Rain splash and wind are true vectors/carriers, yet they are not the only ones on the list. This option is not the key.

3. C

   1, 2 and 4 only

   (c) 1, 2 and 4 only. Birds, dust and wind spread disease, but rain (splash dispersal) is a textbook mechanism too. Omitting 3 is therefore wrong. This option is not the key.

4. D

   1, 2, 3 and 4

   (d) 1, 2, 3 and 4. Birds carry seeds, insects and viruses; dust storms move spores and bacteria; rain splashes inoculum; wind is the main long-distance carrier of many fungal spores. All four spread plant diseases. This option is the official key.

Summary. Official key is (d) 1, 2, 3 and 4. Plant pathogens travel by living carriers and by abiotic media. Birds, blowing dust, rain and wind are all established dispersal routes. No item on the list can be excluded on plant-pathology grounds. Partial combinations that drop rain or dust therefore fail. The Set A key is all four.