高效液相色谱梯度洗脱中的低压梯度又称内梯度,高压梯度又称外梯度。
参考答案:错
解析:低压梯度又称外梯度,高压梯度又称内梯度。
Mother asked the youngest kid _______with his toy car.
A.what the matter was
B.what was the matter
C.what the matter is
D.what is the matter
混凝土芯样试件抗压强度代表值应按一组三块试件的最小值确定。