Answer:
A. Knowing that the attack might reach us in all too short a time, we
immediately began greatly to increase our industrial strength and
our capacity to meet the demands of modern warfare.
Explanation:
The attack is coming quickly so the logical thing to do is to prepare. The other examples are motivational or pathological statements while the first one (A) uses a clear and methodical string of thought to find a solution for the coming attack.
(If a picture type thing helps you: attack coming soon---what do we do?---begin to prepare for the attack immediately.)
The electromagnetic radiation will be high because of the heavy internet usage and might lead to health problems such as a brain tumor and Skin Cancer. The HEV light emitted from the screen of a smartphone leads to severe eye-strain during long-time use and would slowly damage the retina.
The belief that slavery is a morally offensive practice represents MORE kind of social norm.
Answer: an adverb .
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(Note: Adverbs can modify other adverbs.).
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