（）是营养物质向籽粒转运的关键时期。
参考答案：灌浆期
He hurried to the booking office only _____ that all the tickets had been sold out. [ ]
A. to tell
B. to be told
C. telling
D. told
设信道带宽为3400Hz，调制为4种不同的码元，根据Nyquist定理，理想信道的数据速率为______。
A．3.4Kb/s B．6.8Kb/s C．13.6Kb/s D．34Kb/s
