Arrows would continue to fly forward forever in a straight line were it not for gravity, which brings them down to earth.
要不是重力使箭掉落地上,它将会一直沿直线往前飞行。
《柯林斯英汉双解大词典》
2
Once Lion even saw several birds fly in line when he was in an airplane.
狮子还曾经在飞机上看见有几只鸟儿成一直线地飞翔。
3
But neutrinos fly in a straight line: Catch one, and you can trace it back to whatever produced it, which makes them one of the easiest means of probing the far reaches of the universe.