The phrase "function in the disservice of one another" (Lines 7~8, Para. 1) most probably means______.
A. betray each other
B. harm one another
C. help to collaborate with each other
D. benefit one another
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Which of the following is NOT mentioned in the passage as influencing the migration of locusts？
A. Darkness.
B. Agricultural activities.
C. Warm air currents.
D. Overcrowding.
The passage supports which of the following conclusions？
A. The outbreak of locusts in 1938 was more serious than any other in history.
B. Nebraska farmers had no locust problems in the years 1874—1877.
C. There is a possibility that crops in the Unite States might be destroyed by locusts in the future.
D. There is a chance that African migratory locusts may make their way to the United States.
某试样包含四个组分，它们在色谱柱上的分配系数分别为：K1=21，K2=30，K3=59，K4=87。则最先流出色谱柱的组分是()
A. 1＃组分
B. 2＃组分
C. 3＃组分
D. 4＃组分
磷以MgNH4PO4·6H2O形式沉淀，经过滤，洗涤后用适量HCl标准溶液溶解，而后以NaOH标准溶液返滴定，选甲基橙为指示剂，此时磷与HCl的物质的量之比是()。
A. 1：3
B. 3：1
C. 1：2
D. 1：1
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