The important thing is that this is a major breakthrough. “breakthrough” here means an important development or achievement.

 ______ twice a year, whether it is a car or a bus or a truck, is the rule that every driver must obey in this city.

Is this（）longer or shorter?

If necessary to avoid collision or allow more time to（）the situation，a vessel shall slacken her speed or take all way off by stopping or reversing her means of propulsion．

（）means the sufficiency of a vessel in materials，construction，equipment，crew，and outfit for the trade or service in which it is employed.

（）, or drum is used for hauling in or letting out the wires or ropes which will fasten the ship to the shore.

The （） is used for hauling in or letting out the wires or ropes.

Effects which are dutiable or subject to prohibitions or restrictions should be declared in （）.

The（）may examine or re-examine the goods or take samples from them straightaway in the absence of the consignee or the consignor whenever it considers this necessary.

In many installations basket strainers consist of a cylindrical container in which a perforated metal or wire basket is suspendedThe bold and italic word “which” means （）.

As used in this passage，the word “valid” in the second paragraph means______