—Father's Day is coming. Could you tell me ________? —What about a watch? He'll like it.
X、Y、Z、W、R是短周期元素,原子序数依次增大,Y的最外层电子数是次外层的两倍,也是X、W最外层电子数之和的两倍,Z是地壳中含量最多的元素,R的单核离子在同周期元素形成的单核离子中半径最小.以下说法中正确的是( )
“所谓产业革命者,今也其时矣。”这里所说的“今也其时矣”的“时”是指( )