SAT Question b411eb09: Words In Context answer and explanation

English - Words In Context - Fill In Blank Multi Word Phrase
0:00
FREE OFFICIAL BANK
New and interesting research conducted by Suleiman A. Al-Sweedan and Moath Alhaj is inspired by their observation that though there have been many studies of the effect of high altitude on blood chemistry, there is a ______ studies of the effect on blood chemistry of living in locations below sea level, such as the California towns of Salton City and Seeley.
178
Difficulty:Hard
Which choice completes the text with the most logical and precise word or phrase?