[单选]

The original experiment cannot be exactly duplicated.  

Some of the larger birds can remain stationary in the air for several minutes silent。 motionless。 seated。 true。 That uniform makes the guards look absurd.   serious。 ridiculous。 beautiful。 impressive。 The symptoms of the disease manifested themselves ten days later.   eased。 appeared。 improved。 relieved。 The committee was asked to render a report on the housing situation. furnish。 copy。 publish。 summarize。 New secretaries came and went with monotonous regularity. amazing。 depressing。 predictable。 dull。

The original experiment cannot be exactly duplicated.