In which case would testing the null hypothesis not involve a one-tailed statistical test?

In which case would testing the null hypothesis not involve a one-tailed statistical test?

H1: Incentive pay for teachers does affect student achievement

H1: Higher sales tax rates does not reduce state tax revenues

H1: Extending the duration of unemployment benefits does not increase the length of joblessness

H1: Smoking does not reduce life expectancy

I have the above quiz question. Can someone please explain which is the answer and why? I don't understand the difference between which would be one tailed and which would be two tailed.

Thanks.