[单选] 吸入气中C02浓度达20%时，机体会出现（　　）

相关题目:

• [单选] I remember _______ her at the party last week．
• [单选] I have four letters to write today and I have finished_________．
• [单选] His hands _______ a little as he took up a pen and began to write．
• [单选] ________at his model plane over the weekend，he didn’t complete it．
• [单选] I looked and looked，and at last I made out two figures moving slowly in the _______.