of翻译为...的,所以On the 4th Thursday of November.翻译为在11月的4日星期四.in翻译为在,但不是具体的指在什么时候.所以in October翻译为在十月.这种情况下,of等于in.所以
On the 4th Thursday of November.= On the 4th Thursday in November.
People have Thanksgiving Day on the second Monday in October.=People have Thanksgiving Day on the second Monday of October.