Make a short summary of the text.

 

Choose the pairs of opposites.

necessary, to build, to permit, maximum, open, light, possible, to narrow, watertight, high, vertical, limited, impossible, to widen, permeable, low, horizontal, unlimited, heavy, close, forbid, minimum, to damage, unnecessary, dangerous, safe

Choose the pairs of synonyms.

dam, velocity, sufficient, a trough, space, discharge, harm, room, a chute, to allow, structure, release, adequate, speed, embankment, construction, damage, to permit

Fill in the necessary preposition.

1) ___ the design ___ every dam; 2) to prevent smth ___ smth; 3) to be a safety valve ___ smth; 4) ___ the same time; 5) to flow ___ smth; 6) to be constructed __ smth; 7) to be preferred ___ smth; 8) to be required ___ smth; 9) to be available ___ smth; 10) to drop ___ smth.