spontaneous
/spɔnˈteɪnɪəs; spɑn`tenɪəs/ adj
(a) done,happening, said, etc because of a voluntary impulse from within, not caused or suggested by sth/sb outside 自发的; 主动的; 自动的
a spontaneous offer of help 主动提供的帮助
spontaneous applause 自发的鼓掌.
(b) natural, not forced 自然的; 非勉强的
a spontaneous gaiety of manner 天真愉快的神态.