They are cautiously optimistic about the effects of the new medicine.

A. carefully

B. genuinely

C. secretly

D. curiously

Answer: Option A

Solution(By Examveda Team)

Carefully : in a way that deliberately avoids harm or errors; cautiously.
Genuinely : in a truthful way.
Secretly : in a secret way; without others knowing.
Curiously : in a way that shows eagerness to know or learn something.
Cautiously : in a way that deliberately avoids potential problems or dangers.

Synonym of Cautiously is Carefully