应用彩色多普勒技术检查颅内血管，最佳探头频率是（）
A. 2.0MHz
B. 2.5
C. 3.0
D. 3.5
E. 4.0
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What will the tourists do after they return to Beijing Either for departure home or for （）
44()
A. how
B. which
C. why
D. what
Vietnamese people may end the sad story with a smile to ()
A. show affection
B. disguise emotional pain
C. covey politeness
D. show happiness
43()
A. it
B. that
C. what
D. which
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