In English, "它是一根骨头" can be translated as "It is a bone."
This statement refers to an object or an animal body part which is a bone. In English, "it" is used as a pronoun to refer to a non-specific singular object or animal. "Is" is the third person singular form of the verb "to be" indicating the state or identity of the subject which in this case is "a bone." This simple statement can be used to describe the nature or composition of an object or animal part.