Complete the text by choosing the correct option

Half of the world's seven thousand languages [have endangered|endangered|are endangered|was endangered] by lack of human care. As a result, not one language [is swallowed|swallows|was swallowed|has been swallowed] by its "big brother". With the disappearance of the language, all the information in it [is lost|lost|loses|had been lost]. For example, some healing knowledge [keeps|is keeping|is kept|kept] secret by certain African tribes, whose language [is known|is not known|was known|was not known] to others. If a language disappears, stories [tell|are telling|are told|are not told], songs [sing|are not sung|were sung|were not sung], jokes [are not exchanged|are exchanged|exchanged|have not exchanged], the meaning [is understood|understands|is not understood|was not understood], traditions [is observed|have not observed|are observed|are not observed], and culture [is passing|is not passed|is passed|is passed] down from generation to generation. A minority language usually disappears when it [is not protected|was not protected|is not protecting|is protected], [is used|does not use|is not used|is not using] at home, [is not taught|is teaching|is taught|does not teach] at school, [is heard|is not heard|is hearing|does not hear] from parents or old people. As a result, some languages [are known|are not known|know|do not know] to have only three speakers. However, there is hope that more languages [will not be saved|will save|will be saving|will be saved] in the future.