题目

The captain called           his men never to give           before difficulties in the storm. A．on; in       B．for; up      C．at; away   D．out; off 答案：A下列电离方程式中，正确的是（    ） （A）Ca（OH）2 == Ca2+ + （OH）2—             （B）BaCl2 == Ba2+ + 2Cl— （C）H2SO4 == 2H+SO42—                   （D）NaNO3 == Na+ + 3NO—