Complex sentence: Oak Grove School stands out from the other notable institutions of Mussoorie because of two reasons-first of all, it is affiliated to the CBSE, New Delhi, which is rarity amongst the residential schools of Mussoorie.
Split into simpler sentences: Oak Grove School stands out from the other notable institutions of Mussoorie for two reasons. First, it is affiliated with the CBSE, New Delhi, which is a rarity amongst the residential schools of Mussoorie.