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)