Which modern furniture item was invented in 1968 by California furniture designer Charles Prior Hall?

Introduction / Context:
This question tests knowledge about a very popular twentieth century furniture innovation, the waterbed. Linking inventions to their inventors and time periods is a frequent theme in general knowledge exams. Charles Prior Hall, a California furniture designer, is particularly associated with this unconventional type of bed that uses water instead of traditional springs and foam for support.

Given Data / Assumptions:
• The inventor mentioned is Charles Prior Hall from California.
• The year of invention is given as 1968.
• The options list four different types of furniture: sofa bed, captain's chair, waterbed, and hammock.
• Only one of these items is historically connected with Hall in common general knowledge references.

Concept / Approach:
To solve, recall which item was a trendy, somewhat experimental piece of furniture that gained popularity in the late 1960s and 1970s. The waterbed fits this description. Sofa beds and hammocks existed long before the 1960s, and the captain's chair is a style of seating that is not tied to this particular designer. Matching the unusual and time specific nature of the invention to the options leads us to the correct answer.

Step-by-Step Solution:
Step 1: Note the keyword California furniture designer Charles Prior Hall and the year 1968.
Step 2: Recognise that sofa beds and hammocks are much older designs and are not famous as late 1960s inventions.
Step 3: Recall that the waterbed became popular as a symbol of modern comfort and alternative lifestyle in the 1970s, soon after 1968.
Step 4: Understand that the captain's chair is a style of chair and is not linked to a specific single modern inventor in 1968.
Step 5: Therefore connect Charles Prior Hall with the creation and commercial development of the waterbed.

Verification / Alternative check:
Another way to verify the answer is to consider design history. The waterbed appears in many articles on twentieth century interior design, where Hall is named as its creator. It is specifically described as being patented and developed in the late 1960s in California. None of the other furniture items in the options list are described this way, so this consistency check supports the choice of waterbed as the correct answer.

Why Other Options Are Wrong:
The sofa bed is a much older invention and is not uniquely associated with Charles Prior Hall. The captain's chair is a generic term for a certain chair design, not a single 1968 innovation by him. The hammock is an ancient and simple sleeping device used for centuries, so it clearly cannot be a new 1968 invention by a California designer. Thus these options do not match the data given in the question.

Common Pitfalls:
Learners may be tempted to select sofa bed because it is another type of bed and sounds more familiar. Others may guess based only on partial memory of hearing about waterbeds without recalling the inventor. The best strategy is to link time period, region, and novelty. Once you remember that waterbeds were a new and fashionable idea from that era and place, the association with Charles Prior Hall becomes very clear.

Final Answer:
The furniture item invented by Charles Prior Hall in 1968 is the waterbed.