NDA (I & II) 2020 General Ability Test · Question 34 of 148

Correct — B, for. This is a preposition-cloze item. With the present perfect ('have known'), 'for' introduces a length of time ('for a long time'), while 'since' would need a starting point. 'A long time' is a duration, so 'for' is correct.

• (a)since — 'Since' marks the point when something began ('since 2010', 'since Monday'), not a stretch of time like 'a long time'.
• (c)at — 'At' marks a precise moment ('at noon'), not a duration, so it cannot govern 'a long time'.
• (d)before — 'Before' orders events in sequence and does not express how long the knowing has lasted.

This is a preposition-cloze item — 'for' introduces a length of time (for a long time, for two years); 'since' introduces the starting point (since 2010).

No directly related past PYQ was found.

• practice — not a real PYQ

  Fill in the blank: 'They have lived here ____ 2015.'

  • (a)for
  • (b)since
  • (c)at
  • (d)by

  Answer(b) since — a starting point (2015) takes 'since'.

• practice — not a real PYQ

  Fill in the blank: 'We have been waiting ____ two hours.'

  • (a)since
  • (b)for
  • (c)at
  • (d)from

  Answer(b) for — a duration (two hours) takes 'for'.