4) However, he had laid a solid groundwork for others in their attempts to decipher the hieroglyphs.
This is the best answer because it calls the work Young did as "solid groundwork". Options 1, 2, and 3 only report on what Young did, it doesn't show Giblin's opinion of the work as being either positive or negative. In Option 3, Giblin almost sounds negative when he uses the introductory phrase "unable to make fresh progress". The use of the word "solid" to describe the groundwork completed by Young shows a positive view of the work.