【单选题】拮抗多巴胺对以及的β1-受体作用的是( )
【单选题】Don't be discouraged. Have___ try.
【单选题】Don't be discouraged ______ you have fallen behind others.
【单选题】— I'm afraid I have to give it up. — Don't be discouraged. Remember _____ sticks to his work will succeed one day. [ ]
【单选题】— I failed my driving test again. — Don't be discouraged. You'll be successful ________.
【单选题】Don't be discouraged. Have ___ try.