TOEFL Grammar - Choose the right word

in TOEFL Test
Choose the correct word for the following sentence:
The medicine has been shown to _____________________ alleviate the disease's symptoms, even if it does not offer a cure.A. substantial
B. substantially
C. substance
D. substantive
Click here for the correct answer:
The medicine has been shown to substantially alleviate the disease's symptoms, even if it does not offer a cure.
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