Twilight- the soft glowing light from the sky when the sun is below the horizon, caused by the refraction and scattering of the sun’s rays from the atmosphere
Happy twilight- a mother bird is seen singing to her young ones in a soft and gentle voice
Heart of the tree- known as duramen, is more resistant to decay, so that means the tree is less likely to rot.
Personally, i think the topic should have several angles and for it to be specific