less will replace fewer because –
less (Det.) is used with uncountable Nouns to mean a smaller amount of as in-less better/time/importance
and
fewer (Det.) is used with Plural Nouns and a Plural Verb to mean not many as in –
Few people understand the difference.
There seems to be fewer tourists around this year.
Hence, less than ten bags of rice is the right usage

Correct Option: C

less will replace fewer because –
less (Det.) is used with uncountable Nouns to mean a smaller amount of as in-less better/time/importance
and
fewer (Det.) is used with Plural Nouns and a Plural Verb to mean not many as in –
Few people understand the difference.
There seems to be fewer tourists around this year.
Hence, less than ten bags of rice is the right usage

are better off will replace could be better off because – be better off is used for saying that somebody is/ would be happier/more satisfied if he was in a particular position or did a particular thing to have more money.
Look at the examples given below :
Families will be better off under the new law.
She is better off without him.
Hence, you are better off these days is the right usage

Correct Option: A

are better off will replace could be better off because – be better off is used for saying that somebody is/ would be happier/more satisfied if he was in a particular position or did a particular thing to have more money.
Look at the examples given below :
Families will be better off under the new law.
She is better off without him.
Hence, you are better off these days is the right usage

No error.

Correct Option: D

No error.