题目

_________they grow they make sure that what is left in the ground after harvesting_________a natural fertilizer for the next year's crop. A . Whatever; become B . Whichever; become C . Whatever; becomes D . Whichever; becomes 答案：C19．高温下，某反应达平衡，平衡常数K=$\frac{c（CO）•c（{H}_{2}O）}{c（{C}_{2}O）•c（{H}_{2}）}$，恒容时，温度升高，H2浓度减小．下列说法正确（　　）A．升高温度，逆反应速率减小B．恒温恒容下，增大压强，H2浓度一定减小C．该反应的焓变为正值D．该反应化学方程式为CO+H2O═CO2+H2