Why do party balloons rise in air? How high can they go? When do they drift to the ground?
How much water do plants lose? Do they lose it only as water vapour? Can they regulate water-loss?
Which chemical bonds are stronger — covalent or ionic? How can we tell?
Can we grow a dense forest of native species in congested urban spaces or degraded land? How long would this take?
Who were the first people to measure the size of the earth? How did they do it?
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