The Doppler effect (or Doppler shift), named after the Austrian physicist Christian Doppler, who proposed it in 1842 in Prague, is the change in frequency of a wave (or other periodic event) for an observer moving relative to its source.

It is commonly heard when a vehicle sounding a siren or horn approaches, passes, and recedes from an observer. The received frequency is higher (compared to the emitted frequency) during the approach, it is identical at the instant of passing by, and it is lower during the recession.

In this paragraph, what is `relative`?

Six years ago, lawyer-banker-scholar Charles Morris wrote a prophetic book - `Two-Trillion-Dollar Meltdown: Easy Money, High-Rollers and the Great Credit Crunch` - that foresaw the 2008 Great Recession before it clobbered America and the world.

Now Morris has reversed course and sees good times ahead. His forthcoming book, `Comeback,` predicts that surging U.S. energy independence will bring a buoyant rise in American manufacturing and jobs.

The implication of this passage is that you should pay attention to Charles Morris because:

Water polo, or Water ball, is a team water sport. The playing team consists of six field players and one goalkeeper. The winner of the game is the team that scores the most goals.

Game play involves swimming, treading water (using a sort of kicking motion known as `eggbeater kick`), players passing the ball while being defended by opponents, and scoring by throwing the ball into a net defended by a goalie. `Man-up` (or `power play`) situations occur frequently.

Water polo, therefore, has strong similarities to the land-based game of team handball.

Which of the following is NOT a similarity between water polo and team handball?