Option 4 is the right answer. Let us look into the meaning of the given words:
church-- a Christian house of worship.
clock-tower-- a tower specifically built with one or more (often four) clock faces.
temple-- a Hindu house of worship.
alarm-- an anxious awareness of danger.
The sentence talks about the reduction of bus fares which can cause an 'alarm'. The complete sentence is --The drop, though small, is enough to set the alarm bells ringing.