Answer:
a measure of the price of a specified collection of goods and services compared to the price of a highly similar collection of goods and services in a reference year.
Step-by-step explanation:
The changes should be measured that made in the goods and services involved in GDP. The GDP price index would be treated as an indicator for inflation that has been determined by comparing the current GDP to the GDP made in the reference year
So it would be measured the particular collection of the goods & services that should be compared with that of the reference year
hence, first option is correct