What does the second "幅” mean in the following sentence?
&quot;一幅幅&quot; in &quot;一幅幅美丽的山水画&quot; mainly means 'one after another', (indicates plural by extended logic)
一幅幅 is short for 一幅又一幅 or 一幅接一幅 (one after another)
&quot;一幅幅美丽的山水画&quot; means &quot;one beautiful landscape painting after another'
Other examples of double classifier signifing 'one after another':

一個愚蠢的決定 - a stupid decision
一個個愚蠢的決定 - one stupid decision after another

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一個寒冷的冬天 - a cold winter
一個個寒冷的冬天 - one cold winter after another

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一位革命英雄 - a revolutionary hero
一位位革命英雄 - one revolutionary hero after another

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沿途看見一座酒莊 - saw a winery along the way
沿途看見一座座酒莊 - saw one winery after another along the way

'One after another' can describe 'a group of things or people at one time' or 'one individual after another individual across time or distance'
To simply indicate plural, you can use '幾' or '數' as in &quot;幾幅美丽的山水画&quot;