Early cities rely on food and water / from the surrounding countryside, / but today cities often depend on distant sources. / No error

Correct — A, 'Early cities rely on food and water.' The sentence contrasts early cities with 'today', so the first clause describes the past and needs the past tense 'relied' — 'Early cities relied on food and water'.

Why the others are wrong

• (b)
  from the surrounding countryside, — Error-free — a correct prepositional phrase describing the source.
• (c)
  but today cities often depend on distant sources. — Error-free — 'today ... depend' correctly uses the present tense for the present-day contrast.
• (d)
  No error — Wrong — segment (a) uses the present 'rely' where the contrast with 'today' requires the past tense 'relied'.

An error-spotting item on tense consistency — a clause about 'early cities' set against 'today' should be in the past tense to match the time contrast the sentence draws.

No directly related past PYQ was found.

• practice — not a real PYQ

  Spot the error: (a) In the past, farmers / (b) depend on / (c) the monsoon rains. / (d) No error

  • (a)In the past, farmers
  • (b)depend on
  • (c)the monsoon rains.
  • (d)No error
  Answer(b) depend on — 'In the past' requires the past tense 'depended'.
• practice — not a real PYQ

  Fill in the blank: Long ago, people ____ on rivers for transport.

  • (a)rely
  • (b)relied
  • (c)relies
  • (d)are relying
  Answer(b) relied — the past-time marker 'Long ago' calls for the past tense.