1.Ba's hobby/collect stamps
=>BA'S HOBBY IS COLLECTING STAMPS
2.He/start/collect stamps/when he/10 years old
=>HE STARTED COLLECTING STAMPS WHEN HE WAS 10 YEARS OLD
3.Ba often/buy stamps from the post office and/receive stamps/friends
=>HE OFTEN BUYS STAMPS FROM THE POST OFFICE AND RECEIVES STAMPS FROM FRIENDS
4.He/find/collecting stamps/interesting
=>HE FINDS COLLECTING STAMPS INTERESTING
5.He/hope/he/have/more stamps/the future
=>HE HOPES HE WILL HAVE MORE STAMPS IN THE FUTURE