The correct option is C geitonogamy
Transfer of pollen grains from one flower to the stigma of another flower of the same plant is called geitonogamy.
The detachment of a part of the body by an animal under a threatening environment as a defence mechanism is called autotomy. E.g:- lizards cast off their tails.
When the protoplasms of two cells fuse together without the fusion of their nuclei (as seen in many fungi), the process is called plasmogamy.
In cytogamy, two organisms join together without exchanging their nuclear materials. It can be observed in Paramecium.