Which situation is a result of human activities? A. a decay of leaves in a forest adds to soil fertility
B. acid rain in an area kills fish in a lake
C. ecological succession following volcanic activity reestablishes an ecosystem
D. river systems branching off into natural tributaries

An air standard cycle with variable specific heats is executed in a closed system and is composed of the following four processes. 1-2 isentropic compression 100 kpa and 22°c to 600 kpa 2-3 v=constant heat addition to 1500 k 3-4 isentropic expansion to 100 kpa 4-1 p=constant heat rejection to initial state (a) show the cycle on p-v and t-s s (b) calculate the net work output per unit mass (409 kj/kg) (c) determine the thermal efficiency (47.9%)