It's obviously more difficult to swim __ the stream than __

It's obviously more difficult to swim __ the stream than __ It's obviously proven a lot more difficult than a lot of us It __ the workers more than two years to build the hospital. 21.The population of Jiangsu __ to more than twice what it w it's difficult for us __ them.they are stronger than us.(win do you like math? no,it's __ difficult for me to learn it. it is __ to swim in the river in summer.sure it is,look at t 6.32 Matters are very __ .It's very difficult to find a sing the operation proved to be very difficult.it proved to be __ So difficult __ it to work out the problem that I decided to It __ him more than three hours to finish that work. A took The river is very dirty,__ people want to swim in it