--- What do you think of the grammar book?--- Oh, it really is ________ useful reference book, which is worth reading ________ second time.
Mr. Wang has two _____ sons; one has got married and the other has gone abroad.
The workers are pouring _____ steel into the model.
The television is a _____ machine.
Most of the people _____ to the party were famous scientists.
I saw the boy _____ out a moment ago.