Thanks for your reply. I understand the problem you have pointed out, but my confusion was between
base and bases
life and lives
I read in this or some other forum that if we talk about life it should be singular, not their lives as everyone has just one.
And in the "Living in Houston is fun. That's why so many people move here." correction is it required to start a new sentece from that's why? Can't i just use semi colon, or may be and to join it with the earlier sentence?
Bikram
Let me take the easy one first. Yes, you can use a semi-colon, but no, you can't use a comma. When you join two complete sentences with a comma, you have what's called a "comma splice" and that's incorrect. Semi-colons, however, should be used sparingly. There should be a very strong link between the two sentences. It would work here, but make sure you don't have them scattered all over the page, and not more than one in a paragraph. (That's a style tip, not a grammar rule.)
You will find different answers to the singular/plural question, which was at the heart of your original question.
I usually use the plural in things like "It was an experience they would all remember for the rest of their lives." Common sense will tell you what is meant. None of them have more than one life.
Similarly, "The boys introduced their mothers to the teacher" makes you assume that each boy has one mother (although yes, it's possible to have more than one in some situations).
If you read "The boys introduced their mother to the teacher" you would probably assume they were brothers.
Avoid ambiguity by rewriting if common sense doesn't help. "Each boy introduced his mother to the teacher, and then they all had cake." No doubts at all.
So-- the girls all brought their favorite dolls. How many dolls per girls?
How would you write this if there was one doll per girl? How would you write it if there were multiple dolls per girl?