At the age of （）, he had his own lab. A: thirty B: thirtieth C: the thirtieth

The hero of the story is an artist in his ______. A: thirtieth B: thirty C: thirty’s D: thirties

The writer of this novel is a professor in his ____. A: thirty B: thirtieth C: thirty's D: thirties

He began to write poems in his ____. A: thirtieth B: thirty C: thirty's D: thirties

He began to write poems in ______ . A: the thirtieth B: the thirties C: his thirty's D: his thirties

The hero of the story was an artist ______. A: in his thirty B: in his thirty's C: in his thirtieth D: in his thirties