Depending on the test center and the time of year it would be quite possible that you are not going to be using country roads. Not all test centers have access to them and at certain times of the year they could be more hazardous due to ice and pockets of fog.
They have been included in the driving test as a more people die on them than any other road. Any marking will be under the relevant section on the examiners marking form. Make sure you get some practice on them even if your local test center does not use them.
With your speed, drive up to the limit if the road conditions allow it. Be aware of sudden changes in the speed limits. Watch out for road signs and pay attention to the sat nav. It should show the current limit but any speed limit sign outside the car will take priority over any limit shown on the sat nav.