[单项选择]患者，男性，25岁，因不慎从高空坠落致第 4颈椎爆裂性骨折伴脊髓损伤，急诊入院后考虑手术存在较大风险，行颅骨牵引，患者已卧床制动数周，目前患者心血管系统的变化不包括
A. 基础心宰增加
B. 最大摄氧量(VO₂ma增加
C. 易致直立性低血压
D. 易致下肢深静脉血栓
E. 交感肾上腺系统反应不良

Stephen Colbert’s performance at the White House Correspondents Dinner nine days ago has already created a debate over politics, the press and humor. Now, a commercial rivalry has broken out over its rebroadcast.
On Wednesday, C-Span, the nonprofit network that first showed Mr. Colbert’s speech, wrote letters to the video sites YouTube.com and ifilm.com, demanding that the clips of the speech be taken off their Web sites. The action was a first for C-Span, whose prime-time schedule tends to feature events like Congressional hearings on auto fuel-economy standards.
"We have had other hot—I hate to use that word—videos that generated a lot of buzz," said Rob Kennedy, executive vice president of C-Span, which was founded in 1979. "But this is the first time it has occurred since the advent of the video clipping sites."
After the clips of Mr. Colbert’s performance were ordered taken down at You Tube—where
A. it did not want the people to know the message
B. it was forced to do so by the government
C. it did so out of business consideration
D. it was the rival of these video sites