JEE Main Physics question

A student uses a simple pendulum of exactly 1 m length to determine , the acceleration due to gravity. He uses a stop watch with the least count of 1 s for this and records 40 s for 20 oscillations. For this observation, which of the following statement(s) is/are true? [IIT JEE 2010]

• (A)Error in measuring , the time period, is Correct
• (B)Error in measuring , the time period, is
• (C)Percentage error in the determination of is 5%Correct
• (D)Percentage error in the determination of is 2.5%