The idea that "environment is a teacher" is often stated the other way round: children learn from their environment. This is true in a multitude of ways. Babies and very young children learn to take an interest in the world by being placed in stimulating environments. Children learn sophisticated tastes when they are surrounded by objects of beauty. The grand physical environments of famous preparatory schools such as Andover and Exeter inculcate ideals of leadership in elite students.
All the statements from which you have to choose in this question add extra ideas to this simple point, including option d), "Educators must consult with architects when they design an environment for children because it acts like a teacher to children." However, this last option is the only one which preserves the original idea intact as well as adding to it. Option a) changes the idea that children learn from their environment to the rather more obvious point that children learn in their environment. Option b) adds the need for daily change, which is not stated or implied in the original idea. Option c) changes the idea entirely, to focus on indoor environments and diversity. Only option d) states that the environment "acts like a teacher to children." This preserves the original point in almost the same language. The notion that educators must therefore consult with architects is not strictly necessary to the original thought, but is perfectly consistent with it. Option d) is, therefore, the correct answer.