单选题 If said there were about 500, 000 visitors flocking to the city for the 3^rd International Avation and Aerospace Exhibition, that would be a ______ estimate--in fact there are probably a lot more.

A、 constructive
B、 conservative
C、 affirmative
D、 progressive

【正确答案】 B

【答案解析】conservative保守的；constructive建设性的；affirmative肯定的，乐观的； progressive前进的，进步的。