The plumber trained his assistant well. He helped him find a job when his training was through.

Which sentence correctly combines the two sentences?

Although the plumber trained his assistant well, he helped him find a job when his training was through.
The plumber trained his assistant well and helped him find a job when his training was through.
The plumber trained his assistant well because he helped him find a job when his training was through.
The plumber found his assistant a job when his training was through.