单选题 ： Due to his health problems, Richard has to give up _______ hard work on his farm.

单选题 ： Problem solving, like other mental activities such as creativity, is hard to _______

单选题 ： His plan is to design a new model, into which some of previous models will

单选题 ： John has got a rare ability to _______ facts and figures.

单选题 ： Cloud-based tools enable you to engage and _______ with your audience in real-time.

单选题 ： They are working on a new _______ which calls for a(n) _______ amount of time

单选题 ： Life is like a journey with no known _______.

单选题 ： It is amazing that Jack built a robot _______ of his own.