用所给词的适当形式填空  (每空2分，共10分)

小题1:There_________ (use) to be a lot of manatees.

小题2:So far, no man____ (travel) farther than the moon.

小题3:How long ______ you ______ (be) in Ningxia? 

小题4:If it________ (be)a nice day tomorrow, we can go out for a picnic.

小题5:The aggressive animals should _______ (put) in cages.

已知线段a、b、c、d是成比例线段，且a=2cm，b=0.6cm，c=4cm，那么d=______cm．