Questions

‘Unless’ is used to denote the condition i.e. ‘If’...... ‘Not’. So, again the use of negative word ‘not’ is superfluous. So, the phrase, ‘are not very’ needs to be replaced with ‘are very’ to make the sentence grammatically correct. Thus, the correct formation would be, ‘Unless, you are very careful, you will run into debt’.

The more interesting’ needs to be replaced with ‘the most interesting’. This is because, when making comparison between two or more things, the superlative degree is used and not the comparative degree Thus, the correct formation would be, ‘This book is the most interesting of the three’.