Yellow mosaic virus disease of moong spreads by

Answer: Option A

Yellow mosaic virus disease of moong, also known as mung bean yellow mosaic virus (MYMV), is primarily transmitted by the insect vector Bemisia tabaci. Bemisia tabaci, commonly known as the whitefly, is a notorious vector for various plant viruses, including yellow mosaic viruses. It feeds on the sap of infected plants and transmits the virus to healthy plants as it moves between them.

B. Aphir crassivora:
Aphir crassivora is not known to be a vector for the yellow mosaic virus disease of moong. It is not associated with the transmission of this particular virus.

C. Nephotettix viruscens:
Nephotettix viruscens is not known to be a vector for the yellow mosaic virus disease of moong. It is associated with the transmission of rice viruses, not the yellow mosaic virus of moong.

D. None of these:
This option is incorrect since the correct answer is A. Bemisia tabaci, which is known to spread the yellow mosaic virus disease of moong.

Therefore, the correct answer is:
A. Bemisia tabaci