76. All flights _______ called off because of the terrible weather, they had to go there by train.

A．were

B．had been

C．being

D．having been

高茎豌豆的基因组成为DD，矮茎豌豆的基因组成为dd，孟德尔把矮茎豌豆的花粉授给了高茎豌豆，获得杂交后的种子，将杂交后的种子种下去，长成的植株表现性状为[ ]

A．高茎  

B．高茎矮茎各一半  

C．矮茎  

D．高茎多，矮茎少