问题
单项选择题
The underlined word "themselves" in Paragraph 1 refers to ______
A．plant physiologists
B．solutions
C．laboratory flasks
D．roots
答案
参考答案：A
解析：[分析] 细节题型。 见第一段第一句：About fifty years ago，plant physiologists set out to grow roots by themselves in solutions in laboratory flasks，这里指plant physiologists自己培育根用作物；因此themselves在此应为正确选项。