crash*,

(a)  

predict?

(a)  

land?

(a)  

provide?

(a)  

return?

(a)  

launch?

(a)  

discovery?

(a)  

planet?

(a)  

surface?

(a)  

comet?

(a)  

evidence?

(a)  

orbit?

(a)  

crew?

(a)  

do research?

(a)  

on the other hand

(a)  

explore?

(a)  

exist?

(a)  

share?

(a)  

predict?

(a)