下列推理正确的是() A . 离子是带电的粒子,所以带电的粒子一定是离子 B . 同种元素的粒子其质子数相同,所以质子数相同的的粒子一定属于同种元素 C . 氧化物中一定含有氧元素,所以含有氧元素的化合物一定是氧化物 D . 化学变化中分子种类发生改变,所以分子种类发生改变的变化一定是化学变化Since an owl’s ears are widely separated,
______ a slight difference in the time it takes for a
Sound to reach each ear.
A. is there
usually B.
there is usually
C. usually is there D. is usually
there