月季黑斑病常常导致叶片变黄，提早落叶。
参考答案：对
对磁悬浮铁路研究最早的两个国家分别是（）
A.美国和日本
B.德国和法国
C.法国和德国
D.德国和日本
An analyst does research about duration. Which of the following measure is the lowest for a currently callable bond
A. Macaulay duration.B. Effective duration.C. Modified duration.
