When did the worldwide response to ozone depletion begin? select one: a. 1940s and 1950s b. 1960s and 1970s c. 1970s and 1980s d. 1980s and 1990s

The correct answer is:   [b]:   "has no atmosphere" .

The first immigrants to settle in what is now the united states were the ancient ancestors of modern native americans. the precise routes of those first north american immigrants are disputed, but there is no uncertainty about the fact that every human being on the continent is either a recent immigrant or a descendant of earlier immigrants. since the first immigrants came here from asia more than thirteen thousand years ago, there have been four large and easily recognizable modern waves of immigrants into the united states.