Read the following passage and mark the letter A, B, C, or D on your answer sheet to indicate the correct word or phrase that best fits each of the numbered blanks.

Ha Long Bay is ___(1)___ UNESCO World Heritage Site and popular travel ___(2)___ in Quang Ninh Province, Viet Nam. The bay features thousands of limestone karsts and isles in various shapes and sizes. Ha Long Bay is a center of a larger zone which ___(3)___ Bai Tu Long Bay to the northeast, and Cat Ba Island to the southwest.
Ha Long Bay has an area of around 1,553km2, including 1,960 - 2,000 islets, most of ___(4)___ are limestone. The core of the bay has an area of 334km2 with a high density of 775 islets. The limestone in this bay has gone through 500 million years of formation in different conditions and environments. The evolution of the karst in this bay has taken 20 million years under the impact of the tropical wet ___(5)___. The geodiversity of the environment in the area has created biodiversity, including a tropical evergreen biosystem, oceanic and seashore biosystem. Ha Long Bay is home to 14 endemic floral species and 60 endemic faunal species.