**Concept: The question tests on the ability to solve a Word problem**

**Solution:**

The time at which 2 or more people meet at the starting point, is given by the LCM of the time taken by each person to complete 1 round.

LCM of 180, 240 and 300. Take 60 common, and find the LCM of 3, 4 and 10 which is 60

Therefore the LCM is 3600 = 3600 / 60 = 60 minutes or 1 hour**Option D**