The Economist is arguing that it is unlikely that real wages will increase significantly in the near future because the country's businesses are currently investing very little in new technology.
What do we know? We know that if real wages increase then there has been an increase in productivity.
The economists says that this isn't going to happen because there isn't investment in technology.
What does he assume? He's assuming that the only way to increase productivity is to invest in technology. (If we wanted to weaken his argument, we could just say that there are other ways of increasing productivity that do not require investing in technology).
The answer you chose would seem to make sense within the context of the argument, but it would not be the assumption that his argument rides upon.
Hope that helps...