Rachel Carson's famous book, Silent Spring refers to ?

Rachel Carson's famous book, Silent Spring refers to ?
 a) geology of terrain where river originates
 b) ecology and degradation of hot spring due to excessive tourism
 c) biodiversity of an unknown  terrain rich in flora and fauna
 d) the death of songbirds due to eating insects poisoned with pesticides

the death of songbirds due to eating insects poisoned with pesticides