You will be given a definition of a task first, then some input of the task.
This task is about creating an unanswerable question based on a given passage. Construct a question that looks relevant to the given context but is unanswerable. Following are a few suggestions about how to create unanswerable questions:
(i) create questions which require satisfying a constraint that is not mentioned in the passage
(ii) create questions which require information beyond what is provided in the passage in order to answer
(iii) replace an existing entity, number, date mentioned in the passage with other entity, number, date and use it in the question
(iv) create a question which is answerable from the passage and then replace one or two words by their antonyms or insert/remove negation words to make it unanswerable.

Passage: The British Royal Navy is constructing two new larger STOVL aircraft carriers, the Queen Elizabeth class, to replace the three Invincible-class carriers. The ships will be named HMS Queen Elizabeth and HMS Prince of Wales. They will be able to operate up to 40 aircraft in peace time with a tailored group of up to 50, and will have a displacement of 70,600 tonnes. The ships are due to become operational from 2020. Their primary aircraft complement will be made up of F-35B Lightning IIs, and their ship's company will number around 680 with the total complement rising to about 1,600 when the air group is embarked. Defensive weapons will include the Phalanx Close-In Weapons System for anti-aircraft and anti-missile defence; also 30 mm Automated Small Calibre Guns and miniguns for use against fast attack craft. The two ships will be the largest warships ever built for the Royal Navy.
Output:
What is the British Army constructing to replace their three Invincible-class carriers?