文法 G[N]= ( {b} , {N , B} , N , {N→b│bB , B→bN} ),该文法所描述的语言是
·L(G[N])={bi│i≥0}
·L(G[N])={b2i│i≥0}
·L(G[N])={b2i+1│i≥0}
·L(G[N])={b2i+1│i≥1}