Question: In a physical resource block, how many resource-element groups are present in the fourth OFDM symbol of the first slot in a subframe with extended cyclic prefix?
Option 1: Two
Option 2: Three
Option 3: Four
Option 4: Five
Explanation: According to the text, in the fourth OFDM symbol of the first slot in a subframe with extended cyclic prefix, there are two resource-element groups in physical resource block consisting of resource elements with l=0 and l=2, respectively.