Concepts: beat, heart, smile
A: little girl smiling as the doctor checks her heart beat with a stethoscope
Concepts: roll, snowball, snowman
A: Four children are rolling snowballs in a yard to make a snowman.
Concepts: appear, track, train
A: A train is moving along on a track that appears to lead right into the snowy mountains.
Concepts: ecosystem, live, organism
A:
an ecosystem is a community of organisms and the physical environment in which it lives .