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-- Did you read a book about customs last week?

-- Yes, I found ______ very useful to know the customs of foreign countries.

A. that???????????? B. this???????????? C. it’s??????????? D. it

I found _____ very difficult to learn  maths  well.

I found _____ very difficult to learn  maths  well.

A．what             B．it                C．that              D．this

-- Did you read a book about customs last week?

-- Yes, I found ______ very useful to know the customs of foreign countries.

A. that             B. this             C. it’s            D. it

After visiting different countries, I found _______ very important to learn about table manners.

A. it                B. that            C. this              D. us