单项选择题

Sound waves reflected from a hill can be used to calculate the______.

A．Speed of sound
B．time between a sound and ifs echo
C．height of the hill
D．distance of the hill
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单项选择题
What was the speaker's purpose in sharing the story about his grandfather
A．To highlight the difficulties of finding affordable housing in the future.
B．To illustrate older people's loss of identity and self-worth.
C．To describe the lack of public facilities designed for the elderly.
D．To justify that self-worth is often tied to one's profession and social standing.
单项选择题
What is the main topic of this speech
A．The growing crisis of inadequate retirement pensions for the future.
B．The problem of providing adequate medical care for the elderly.
C．The need to reevaluate our attitudes towards senior citizens.
D．The need to reform the present pension system.
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