题干
I will take my parents to the museum ________ it doesn't rain this afternoon.
A：or
B：if
C：so
D：and
答案(点此获取答案解析）
B
I will take my parents to the museum ________ it doesn't rain this afternoon.
A：or
B：if
C：so
D：and
，到那时太阳向外辐射的能量是由上述两种核反应共同产生．若已知
的质量为m1，
的质量为m2，则下列判断正确的是
