层位关系是指堆积单位与堆积单位之间的关系。（）
A、上下
B、早晚
C、前后
D、叠加
参考答案：D
Before graduation, we had a lot of practical _____ by doing a part-time job in the company and it was
really _____ for us.[ ]
A. experience; a great experience
B. experiences; a great experience
C. experience; great experience
D. experience; great experiences
已知两株高茎豌豆的基因组成都是Dd，把二者相互杂交，后代的性状表现和比例为（ ）
A．高茎：矮茎=1：1
B．高茎：矮茎=2：1
C．高茎：矮茎=3：1
D．高茎：矮茎=4：0
