Which of the following are likely to be sources of increasing productivity?

1) Substitution toward labor and away from capital (with constant technology)

2) Better trained labor

3) increases in technology know how

A) 1 only

B) 2 only

C) 3 only

D) 1 and 2 only

E) 2 and 3 only

I had this question and my selection was A) 1 only but this answer was wrong. Can you tell me the correct answer and why? Thank you