The weather turned out to be fine yesterday. I ________the trouble to carry my umbrella with me. 

A．should have taken

B．could have taken

C．mustn't have taken

D．needn't have taken

股票所载有权利的有效性是始终不变的，因为它是一种无限期的法律凭证。股票的有效期与公司的存续期相联系，两者是并存的关系。这是指股票的( )特征。

A．永久性

B．持续性

C．参与性

D．收益性