AB是圆O的直径,点C,D都在圆O上,连接CA,CB,DC,DB.已知∠D=30°,BC=3,则AC的长是____ .
I ask you to sit down ___________ table, not to sit down ___________ the table.
选出句子中你所听到的单词或短语( )
(从上到下依次填写)