This was one of my experiences (1) . When

题目：

This was one of my experiences (1) . When I was in my 30s, I was working for a large international company which had its head office in London. I was working in the (2) department.
The company had a training centre which was just outside London. Different courses were held there throughout (3) and I (4) go on one training course a year. These usually started (5) a Sunday evening and lasted six days.
Once I was (6) a week’s training course with about forty (7) sales people. I was in the bar on the Friday evening and suddenly a woman who was (8) behind the bar asked mea curious question. "I hope you don’t (9) my asking," she said, "but I’ve been (10) about it all week. Have you got a sister (11) Mary" The woman’s name was June. And she used to do various jobs at the training centre. She worked in the office, she organized all the food and drink for the centre and she worked in the bar at lunchtime and in the evening.
My answer (12) June’s question was "Yes", and June said, "I thought (13) . I met her last September when she was organizing a course here. " At that time, my sister was working for (14) company but in a different part of the country. That was (15) she came to be at the training centre.
(16) surprised me was how June guessed we were brother and sister. Three things made it even more (17) . First, she had met my sister six months before she met me. Second, they have about sixty new people every week at the training centre. So about one thousand five hundred people had (18) the centre in those six months. And (19) , my sister is married, so she doesn’t have the same family name as me.
We’re not (20) , but I guess we must look quite like each other.

A．where
B．when
C．what
D．how