Hello, eeky. I have some further questions.
A couple of comments...
(8a) We seldom worry about drinking water.
(8b) We rarely worry about drinking water.
(8c) We hardly worry about drinking water.
It may not matter, but these are potentially ambiguous as to whether "drinking water" refers to water that is fit to drink or to the activity of drinking water.
How about these?
(8d) We seldom worry about water for drinking.
(8e) We rarely worry about water for drinking.
(8f) We hardly worry about water for drinking.
I guess (8d) and (8e) have almost the same meaning, but (8f) is a little different from the others. Am I right?
(9) Not everyone in the world live peacefully.
Should be "lives" (or some other fix).
Yes. I did make a mistake.
(10) "What's this?" " I have no idea."
Minute typo: superfluous space.
"What's this?" "I have no idea."
Is this OK?
(15) There are few people who [/that] know this.
Both "who" and "that" are used to refer to people, but for me "who" is more elegant.
Elegant. OK.
(17a) I came to know how my sister keeps fit.
(17b) I got to know how my sister keeps fit.
Correct English, but does not seem a massively likely thing to say. Depending on the required nuance, "I found out how my sister keeps fit" might be more likely, for example.
The original sentences go like this:
My sister asked me if I wanted to jog with her. I wondered how far she would run.
After an hour's jogging, I came to know how she keeps fit.
Is it still unnatural?
(21) Nobody knows how far you will run.
Correct English, but seems a slightly unusual thing to say. What is the envisaged situation?
How about this?
(21b)Nobody knows how far you've run so far.
(22a) I hardly know how people around the world live every day.
(22b) I scarcely know how people around the world live every day.
Correct English, but the meaning is not terribly clear. Are you talking about how people manage to survive, or how they spend their daily lives?
(22a) is from the textbook we use. If it is ambiguous, how would you suggest I should correct it?
How about this?
(22c) I hardly/scarcely know how people around the world spend their daily lives?
I cannot see more than one possibility for any of (24) to (33).
Questions (34) to (31) all seem OK to me. In (39), "the senior citizens" refers to a specific group of senior citizens. If you mean senior citizens in general then delete "the".
You mean (34) to (41), right?
Ahh, I see. I should not have put "the" before senior citizens.
Thanks in advance.
Hirashin