Describe how a zygote with trisomy 21 is likely to occur during ferlilization

B and E

Explanation:

Social behaviour is described as interactions taking place between two or more individuals with in the same species.

The interactions outside the species are not considered part of social behaviour.

Thus, out of all given options, option B and E are correct.

Option A, D and C , are not correct because with in animals itself there are millions of species and thus interaction with in the species is not considered as social behaviour.