根据以下材料，回答题
I had always known that the Chinese NewYear was different from our own but otherwise assumed that the way we Europeansdivided up the year was something in common. Quite recently, though, I foundout that there used to be some pretty dramatic differences. During the MiddleAges, the official start of the year varied enormously within Europe. In Spain,Portugal, Switzerland and Germany it began on Christmas Day, whereas it startedon the 1st March in Venice and the 21st in England. In Rome, it was at one timethe 25th January but then changed to the 25th March. In Russia the new yearcoincided with the spring equinox (春分).
If this isn′t complicated enough the Frenchused to start their official year from Easter day. Easter, as I am sure you allknow, is a moveable feast whose complicated calculation is quite a mystery tome. However, this French style of working out the beginning of the year led tosome years being as short as three hundred days while others could stretch tofour hundred with two spring times with one at each end!
With all these different dating systems inoperation you can imagine the enormous potential for confusion. This can createheadaches for students engaged in studying the period from original documentsas they can actually find somebody′s death being recorded months before theyare married and battles still being fought weeks after a peace agreement hadbeen signed! It would all depend on where the events had been recorded. As anactual example the student could easily get muddled (糊涂的) over the date of thefamous trial of the Knights Templar in Paris. According to records this longand complex trial ended in 1313 as the New Year didn′t officially start untilthe 7th April. Fortunately for all of us these differences were eventuallysolved. In December 1564 the French decided to start the New Year from the 1 stJanuary. The Russians adopted this new style of dating in 1725 and the Englisha further twenty-seven years later.
A.had always known about the dating systems
B.knew Europeans varied in their datingsystems
C.had just found out about the Chinese NewYear
D.had been forced to revise his opinion