Interested in Language
I. If you can read a clock, you can know the time of day.
I think there should have "a" or "the" before "day". Or, chang "day" to"days". Right?
II. AIDS is a life-threatening sickness that attacks the body's natural defense system against disease. It can destroy the body's ability to protect itself.
If I replace "It" with "The sickness", would the sentence be better?
the two sentences are fine as they are
'time of day' is a fixed expression, that is why you don't need an article here.