Knowledge, skills, and experience are examples of capital.
a.
hypothetical
b.
undesired
c.
physical
d.
human

Lets evaluate
A. hypothetical, hmm, hypothetical is like a guess, so not

B. undesired, no you want skills and knowlege

C. physical, not really, physical is like money or cars or stuff you can touch and count, you can't count knowlege or skill

D. human capital refers to the stock of knowledge, only people can have, like creativity, it is definitly this choice

D is answer

Europeans are more concentrated in urban areas.