计算：1﹣（﹣3）=____
—________ will you ask for help when you get into trouble?
—My parents, I think.
—Oh, I couldn't feel . I made few mistakes in it.
南极考察队队员在地球南极附近用弹簧秤竖直悬挂一还未通电的螺线管，如图所示，下列说法正确的是（ ）
