Reaction of furan with chloroform in base
The key to this question lies in realising that the Reimer–Tiemann reaction is not an electrophilic aromatic substitution but it is in fact


  addition of a carbanion to a strongly electron-deficient carbene.


This was discussed by @KlausWarzecha and @ron in answers to a previous question.

Therefore the major product will be the one where the attack comes from the carbon with the greatest electron density. Using MolCalc (partly developed by @JanJensen) I generated an electron density plot of furan which clearly shows that there is more electron density on the 3 and 4 carbons than on 2 and 5. This explains the given major product.