Toys that are considered eco-friendly are those that _______________
Promote interest in preserving the natural environment
Help the development of social skills
The correct option is D Use natural materials
The given sentence are completed using the words "use natural materials" as suggested by the lines "Another crucial factor is eco-friendliness ... best pro-environment design processes ... uses wood and colours ... from natural materials." Hence option B is correct.
It is not mentioned anywhere that eco-friendly toys promote interest in preservation of the environment, hence A is incorrect.
(In fact, "toy design has to be conscious about ethics and values..." So the cultural ethos are kept in mind, and not the environment.)
Toys on the whole are designed to develop a child's social skills, not toys that are particularly eco-friendly: "Toy design... aid their cognitive, physical, emotional and social skills." Hence C is incorrect.
No mention of fibre is made in the paragraph, only wooden toys are mentioned. Hence option D is incorrect.