Complete each of the following sentences with the correct form of the words given below.

Complete each of the following sentences with the correct form of the words given below.
1,I lost my keys and could not ___ the door.(lock)
2,Mary was already an______-primary school teacher at the age of 25.(experience)
3,Their lives were frequently______by gas explosion.(threat)
4,The first American ______ of this opera was in 1926.(perform)
5,The boy is______ to have had the help and guidance of such a learned uncle.(fortune)
6,You will increase your______ if you introduce more system into your work.(efficient)
7,If you use this chemical to clean your shirt,the stains will ______ immediately.(appear)
8,John and Mary had a______ ,but they have made it up now.(understand)
9,The children looked wonderfully______ with their bright eyes and glowing cheeks.(health)
10,Looking up,I saw his eyes fixed on me in______ .(curious)