The key answer of exercise 2

a)

| know

• I'm pretty sure
• I know it like the back of my hand
• I know it by heart
• I know it inside out
• I'm fairly certain it is
• I'm positive it is

I don't know

• I haven't a clue
• I don't know off the top of my head
• I don't know offhand
• I've never heard of him
• I know next to nothing about it
• I haven't the faintest idea

b)

• I'm pretty sure means 'I'm quite certain'.
• I don't know off the top of my head and I don't know offhand are similar. They mean 'I can't tell you the answer now (without looking for the relevant information)'.
• We use I've never heard of ... when we don't recognise the name of the thing mentioned (it could be a person, an object, a place, etc.).
• We use next to nothing when we recognise the name of the subject, but know almost nothing about it / him / her. We use this expression in response to a 'What do you know about ...?' question, or in the expression 'I know next to nothing about it.'
• I know it like the back of my hand is often used to talk about a place, while I know it inside out is often used to talk about a subject. I know it by heart is used for something we have memorised, perhaps a poem or a speech.
• The strongest are: I know it like the back of my hand, I know it by heart, I know it inside out, I haven't a clue, I haven't the faintest idea.
• The expressions with a similar meaning are: I know it like the back of my hand, I know it by heart and I know it inside out. They mean 'I know it extremely well'.