(﹣3)+(﹣4)﹣(+11)﹣(﹣19)
解:原式=﹣3﹣4﹣11+19=﹣18+19=1.
文物是历史研究的重要对象。结合如图分析,对该文物理解正确的是( )
—Your teachers' idea is right. The more friends you make, ______ you will be.
①4NH3(g)+5O2(g)⇌4NO(g)+6H2O(g)△H=﹣905kJ/mol
②4NH3(g)+3O2(g)⇌2N2(g)+6H2O(g)△H=﹣1268kJ/mol
下列说法中不正确的是( )