(1) A few people say bad things about Jim.
→ Few / Only a few / Very few
(2) Husbands who take childcare leave are increasing.
→ More and more husbands are taking [take] childcare leave.
(3) The number of traffic on this road is increasing year by year.
(4) The number of students who study abroad are decreasing.
→ Fewer and fewer students are studying [study] abroad.
（別解）The number of tudents who study abroad is decreasing.
(5) There is the White House in central Washington, D.C.
→ The White House is (located) in cenyral Washington, D.C.
（解答）A lot of [Many] Japanese (people) believe (that) their blood type has something to do with their character.
（別解）A lot of Japanese (people) believe (that) their perspnality is influenced by their blood type.
（解答）No one [Nobody] has ever seen Santa Claus, but this dose not prove that he does not exist.
（別解）No one has ever seen Santa Claus. However, this is not proof that he does not exist.
（解答）Very few [Only a few / Few] Japanese people blow their nose with handkerchief.
（別解）There are very few Japanese people who blow their nose with a handkerchief.
（解答）In recent years, the amount of farmland [land that is used to grow crops / land that is used for farming] in the world has been decreasing.
（別解）These days, cultivated land in the world is becoming less and less.
（解答）These days [Nowadays], more ando more people are reading e-books [electronic books / digital books].
（別解）These days, the number of people who read e-books is increasing rapidly [quickly / fast].
（解答）It is a pity [a shame] that a lot of people [many people] still mistakenly believe that as long as they speak English, they can be internatinally-minded.
（別解）Unfortunately, alot of people still believe that they have only to speak English to be internationally-minded, but they are wrong.
（解答）The mount of CO2 in the atomosphere is increasing and this is causing global warming.
（別解）The amount of carbon dioxide in the atomosphere is increasing, which is making the earth warmer (and warmer).
（解答）Even if [Even when / Even though] there si an announcement that asks people to offer [ to give] their seats to elderly people on trains or buses, many of them (will) ignore it.
（別解）Even if a train conductor asks passengers to offer their seats to elderly people, many of them do not do it.
（解答）Nowadays, more and more people want to take their pets wherever, so places that can be entered with pets are becoming more popular.
（別解）Nowadays, more and more people wnt tp rake their pets wherever they go. As a result, places that owners can go with (their) pets are gaining popularity.
（解答）It seems that parents these days allow their children to play computer games, partly because they themselves also played them when they were children. In fact, I hear (that) many of them play them with their children on their days off.
（別解）These days, parents do not mind their children playing computer games. One of the reasons for this is that they themselves used to. In fact, I hear that many parents spend their holidays playing games with their children.