निम्नलिखित में से किस तिथि को आर्कटिक वृत्त (Arctic Circle) पर लगातार 24 घंटे का दिन (प्रकाश) रहता है?

If the Earth's axis were not tilted, which of the following changes would most likely occur?

What name is given to the imaginary great circle that divides the Earth into the illuminated hemisphere (daytime) and the dark hemisphere (nighttime)?