Correct answer: C. Grand Trunk Road and currency system
Explanation: The direct answer is option C: Sher Shah Suri is famously associated with the Grand Trunk Road and an improved currency system. Administrative efficiency means organising the state so that travel, communication, trade, taxation and government work become more reliable. Sher Shah repaired and developed important roads, including the route later known as the Grand Trunk Road, and established facilities such as rest houses and arrangements that helped travellers and officials. He is also associated with the standard silver coin called the rupiya, which made payments and revenue collection more uniform. Together, roads and currency supported trade, administration and military movement. Option C is correct because both examples are widely linked with Sher Shah Suri's practical administrative reforms. Option A is wrong because an astronomical observatory is not the famous example normally used to describe his main administrative achievements. Option B is wrong because the council of eight ministers, or Ashtapradhan system, is chiefly associated with Shivaji, not Sher Shah Suri. Option D is wrong because a religious experiment is not the standard evidence for Sher Shah's administrative efficiency; his reputation is especially connected with roads, revenue arrangements, currency and governance. The safest exam method is to connect Sher Shah with roads, sarais, currency and efficient administration. Memory cue: Sher Shah means road plus rupiya—better movement and more organised money.