—The boy can speak both English and Japanese _________ he is only ten.
—Wow, what a clever boy!
A:if
B:because
C:although
34+20=____
68-30=____
28+40=____
84-50=____
546减去138的差,再除以4.商是( )
用化学知识解释下列问题:
(1)铝是一种活泼金属,但铝制品却不易锈蚀,其原因是____ ;
(2)在建筑工地上,我们常常看到:傍晚下班前,工人师傅通常在用剩的石灰浆上覆盖一层沙土,以便第二天再用,其原因是____ .