A:did you realize
B:that you realized
C:did you not realize
D:that you didn’t realize
咏“山”:____,____。(李白《望天门山》
We found necessary to protect the environment.
农作物所必需的营养元素有碳、氢、氧、____、____、____、钙等,其中____、____、____是最主要的化学肥料。化学肥料是指____。
当显微镜视野很暗,影响观察时,应调节光亮程度,此时应采取的措施是( )