I haven't seen _______ this since I began to collect stamps.
A:as old a stamp as
B:as an old stamp as
C:an old stamp such as
D:a such old stamp as
某同学用天平和量筒测量小石块的密度。(1)测量原理是____ ;(2)图(a)中A—F为测量小石块质量、体积过程中的几个情境,有一处错误是____ ,排除错误后合理的顺序是____ ;(填字母)(3)图(b)可知,小石块的质量是____ g;(4)由E、F过程可知,当量筒中水静止时石块的体积为____ mL,则小石块的密度为____ kg/m3。
5+94-49=____
____、____
青蛙的发育是变态发育,幼体和成体相比较,其形态上的差异主要表现在( )
用化学用语填空:(1)三个氢原子____
(2)两个五氧化二氮分子____(3)3个氢氧根离子____
(4)氧化镁中镁元素为+2价____