the position he wants to apply is very important A to which

B
apply sth to sth 是指把某某物应用在某某上,比如说
we can apply this new technology to our new product
但是注意,因为这里的to是做介词用,所以如果要在to后面用动词,必须用动词的ing形式.
而apply for是申请某职位,某证明,某奖学金等等
比如说 I want to apply for the scholarship of this school.