—Does your school hold the raising of the national flag every Monday morning? —Yes, it rains heavily.
A:if
B:since
C:because
D:unless
+(﹣7)=____,﹣(+1.4)=____,+(+2.5)=____,﹣+(﹣5)=____;﹣﹣(﹣2.8)=____,﹣(﹣6)=____,﹣﹣(+6)=____.
关于我国自然资源的说法正确的是( )