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1. in a hot-water heating system, room temperature is controlled by a device called
2. heat engines convert which type of energy into mechanical work?
a. chemical
b. nuclear
c. thermal
d. elastic
3. how are internal combustion engines different from external combustion engines? give examples of both types of engines.

the cladogram shown here shows similarities and differences among several classes of vertebrates. anatomically, the four have limb structure as their common ancestor. we might separate the mammals from the other three classes because they a) divergent; do not lay eggs b) identical; are warm-blooded c) varied; a four chambered heart d) homologous; have mammary glands