I must wash the dishes. Я должен мыть посуду.
I must tidy my room. Я должен убирать мою комнатую
I must do my homework. Я должен делать мою домашнюю работу.
I was doing some housework when I found our old family aibum.
r) Past Continuous + Past Simple.
The term “internal combustion piston engine” referS to engines in which air and gasoline are buRNT inside the metal cylinders and which drive rotating crankshaft by means of piston and connecting rods. Since a great deal of heat IS produced when the gasoline mixture burns or explodes, some means must be provided to CARRY away the excessive heat. According to the cooling system employed the piston engines may BE CLASSIFIED as air-cooled engines and liquid-cooled ones.