To be honest, he didn't tell any of us about his coming, he just showed up _ in the morning.A. by all meansB. out of the blueC. in the same boatD. at this rate

这道题考察的是对英语习语的理解。题目中提到他没有告诉任何人他要来，只是在早上突然出现了。这表明他的到来是出乎意料的。选项中，A. by all means 意为“无论如何”；B. out of the blue 意为“出乎意料地”；C. in the same boat 意为“处于同样的困境”；D. at this rate 意为“照这样下去”。根据题意，B选项最符合题意。