After determining the levels of calcium carbonate and the types of fossilized algae present in core samples taken from

[BTGmoderatorDC]

After determining the levels of calcium carbonate and the types of fossilized algae present in core samples taken from the bottom of Lake Titicaca in the Andes, a group of scientists was able to reconstruct the history of precipitation in tropical South America over the past 25,000 years.


A. the types of fossilized algae present in core samples taken from the bottom of Lake Titicaca in the Andes, a group of scientists was able

B. the types of fossilized algae that are present in core samples taken from the bottom of Lake Titicaca in the Andes, it was possible for a group of scientists

C. the types of fossilized algae that had been present in core samples taken from the bottom of Lake Titicaca in the Andes, that made it possible for a group of scientists

D. what types of fossilized algae had been present in core samples taken from the bottom of Lake Titicaca in the Andes, it was possible for a group of scientists

E. what the types of fossilized algae were present in core samples taken from the bottom of Lake Titicaca in the Andes, a group of scientists was able


OA A

Source: GMAT Prep

[deloitte247]

This sentence explains that after determining the levels of calcium carbonate and what type of algae is in the Titicaca, a group of scientists were able to reconstruct the history of precipitation in tropical South America over the past 25000 years.

Option A - Correct
This correctly introduces the subordinate clause, which in turn refers to the group of scientists.

Option B - Incorrect
In the sentence, the use of 'algae that are present' throws the sentence off the course of its expression, it modifies correctly. It is supposed to modify "the scientist, determined the level of calcium carbonate and the types of algae present in the lake"; hence, it modifies a non-existent word.

Option C - Incorrect
This option is structurally inappropriate. The use of the incorrect test of the verb "had been" in the sentence is wrong.

Option D - Incorrect
Using 'what types...' in the sentence gives the sentence an illogical representation and it doesn't make it parallel to the levels of calcium carbonate.'

Option E - Incorrect
It has issues with parallelism. There is no correct comparison between "the levels of calcium carbonate" and "what the type of fossilized algae."