Good Riddles

Question: You have a flashlight that takes 2 working batteries. You have 8 batteries but only 4 of them work.

What is the fewest number of pairs you need to test to guarantee you can get the flashlight on?

Question: I have two rings. I move by request. If the mixture isn't right I just sit and rest.

What am I?

Question: I go up and I go down,
towards the sky and the ground.
I'm present and past tense too,
Let's go for a ride, me and you.

What am I?

Question: A cheap man and his wife decide to go on a trip for their 10th anniversary. They go to Brazil and while touring the rain forest his wife falls off of a bridge to her death.

Shortly after her death one of the flight attendants on their flight sees a report on her death on television. She immediately calls the police and tells them the man murdered his wife.

How did she know?

Question: You can easily touch me, but not see me.
You can throw me out, but not away.

What am I?