问题

For more than a decade, experts from across the globe ________ on the cure of the disease that way

A:worked
B:are working
C:have been working
D:were working

正确答案是：

同类题型

The lesson Mr Li gave just now was too difficult for the class to ________

_ from view day by day, the singer isiturning to his memories for comfort

Would you ever let him work hereagain—!Not after the way he treated me

I don’t like to be interrupted if I_____

The iphone 4s, ________ by Apple, sells well across the world.