Select the most appropriate option to fill in the blank.
Scientists all over the world are engaged in ______ how to find a vaccine for COVID-19.

Correct option is A

The correct option to fill in the blank is (a) researching.
Explanation: The word "researching" fits the context as it refers to systematic investigation to discover facts. (अनुसंधान करना)
Example: Doctors are researching the effects of the new drug.
Meanings of other options:
· (b) scrutinizing: To examine closely. (बारीकी से जांचना)
· (c) investigating: To carry out inquiry. (जांच करना)
· (d) inspecting: To look carefully for assessment. (निरीक्षण करना)