The initial design and construction of which massive temple took place during the reign of Suryavarman II

a) Shri Mariamman Temple

b) Angkor Vat

c) Batu Caves Temple

d) Kamakhya Temple

The temple of Angkor Wat was dedicated to the Hindu God Vishnu  by King Suryavarman II, who reigned between Ad 1131 and 1150. the temple was  constructed over a period of 30 years, and illustrates some of the most beautiful examples  of Khmer and  Hindu art.  Covering  an area of about 81 hectares, the complex consists of five towers, which are presently shown on the Cambodian  national flag.

Therefore option (b) is the correct one.