Select the most appropriate option to fill in the blank.

My cousin’s study on the reading habits of school children across three states has been recognised as a ______ piece of research.

pioneering

The most appropriate option to fill in the blank is pioneering.

The word "pioneering" means to be the first to do something new or innovative. It is the most appropriate word to use in this context, as it conveys the meaning of the cousin's study being groundbreaking and significant.

The other options are not as appropriate.

• Negligent means careless or uncaring. This is not the right word to use, as it does not make sense to say that the cousin's study was negligent.
• Proud means feeling satisfaction or pleasure as a result of one's own achievements. This is not the right word to use, as it is not necessary to say that the cousin is proud of his study.
• Useless means having no purpose or value. This is not the right word to use, as it does not make sense to say that the cousin's study was useless.