I ___ so busily recently that I ______ no time to help you with your math. That’s OK. I can manage it by myself.
A. have been working; have
B. have worked; had
C. am working; will have
D. had been working; had had
查看答案
He ____ at the meeting, but his heart attack prevented him.
A. will speak
B. is going to speak
C. had to speak
D. was going to speak
I ____ ping-pong quite well, but I haven’t had time to play since the New Year.
A. will play
B. have played
C. played
D. play
翻译的产物是
A. 戊糖
B. 核酸
C. 蛋白质
D. 氨基酸
蛋白质生物合成中，多肽链上氨基酸的排列顺序取决于
A. 相应tRNA的专一性
B. 相应氨酰-tRNA合成酶的专一性
C. 相应tRNA上反密码子排列顺序
D. 相应mRNA上密码子排列顺序
微信支付 
支付宝支付