Math Help - Regression analysis

Don't know if this is the right place to ask, but I'm stuck on a question which hopefully is quite simple. I've got one dependent variable (let's call it A, which is on a ratio scale) and six independent variables (B - G). It's clear that these independent variables are affecting the dependent one. The question is:

If we want to choose just one of the independent variables to predict A, which one should we choose?

This should be done in a computer program and I'm not asking for any calculations, but I'm wondering what approach I should use? The teacher (who is on a vacation, which is why I can't ask him this) told us to do a regression analysis, but could you just do a linear regression to answer the question? Since the question contains the word prediction, I was thinking of doing a logistic regression, but that is of no use when the dependent variable is on a ratio scale, right?

Thanks in advance for your help! Much appreciated.