Why does the Leaning Tower of Pisa in Italy lean? It leans because of a mistake. It has leaned almost since the day the builders b____ it.
In 1774, the people of Pisa in Italy wanted to build a bell tower. They wanted the tower to be the m____beautiful bell tower in Italy. The city needed a bell tower because the church(教堂) did not have o____ . As soon as the first floor of the building was finished, the tower started to lean. Builders t____  to make the building straight again as they added more floors, but the leaning tower got w____ as the tower grew. It took about 180 years to finish the tower. Today, the leaning tower has eight f____  It is 54.5 meters t____. And it leans almost 4 meters to one s____ . The tower is also sinking(下沉) into the g ____ on which it was built. Every year, the tower leans a____ 1.7 cm.

计算： ${\left(-5\right)}^4$= ____； $-5^4$= ____； ${\left(-\frac{2}{3}\right)}^3=$ ____．

500mL KNO₃和Cu(NO₃)₂的混合溶液中c(NO₃^－)＝6.0 mol·L^－1，用石墨作电极电解此溶液，当通电一段时间后，两极均收集到22.4 L气体（标准状况），假定电解后溶液体积仍为500 mL，下列说法正确的是（   ） 

请根据下列实验装置图回答问题．