Bom dia, vamos começar!
Não sou nenhum professor mas vou tentar te ajudar, caso identifique alguma informação errada ou fique com dúvidas é comentar.
Basicamente, você vai identificar o comparativo quando encontrar dois substantivos de mesma classificação, como duas frutas ou dois animais, e superlativo quando este substantivo estiver acompanhado somente do adjetivo.
Para o comparativo há dois casos:
O caso do adjetivo grande (com mais de 5 letras) - em que será coloca "more" antes do adjetivo e adicionando "than" logo depois:
1 - My sister is more intelligent than my brother.
E o caso do adjetivo pequeno (com até 5 letras) - em que será utilizada a mesma regra do "than" depois do adjetivo, além da modificação do adjetivo finalizado com "er"
3 - Iceland is colder than Spain.
Para os superlativos há dois casos:
Utilizar "the" antes do adjetivo e modificar este finalizando com "est"
2 - The blue whale is the biggest animal.
E o caso do adjetivo grande em que se usa "the most" antes do adjetivo sem modificações:
28 - It's the most expensive hotel in Swiss.
Agora vamos para os outros exercícios:
4 - This is the worst book I've ever read. (Atenção que algumas palavras como "good" e "bad" terão modificações um pouco mais drásticas)
5 - My neighbour is the luckiest person I know.
6 - Friday is the busiest day of the week.
7 - These trainers are much cheaper than those.
8 - Frank works harder than most people.
9 - I'm better at English than you. (Cuidado com a posição do "than")
10 - Today has been the hottest day of the year. (Hot é composto por Consoante Vogal Consoante, então sua última letra será dobrada)
11 - This is the worst CD I've ever listened. (Novamente o bad com uma mudança fora da regra)
12 - English is easier than Japanese.
13 - Which mountain is the highest in the world?
14 - John is more clever than his brother.
15 - English is more useful than Latin.
16 - What is the most common word in English?
17 - The Nile is the longest river in the world.
18 - This is my oldest brother. Mary is their oldest daughter. (Não há "the" nessa frase pela presença de "my" e "their")
19 - That skyscraper is one of the tallest buildings in the city.
20 - The first exercise was easy but this one is more difficult.
21 - Our journey took longer than we expected.
22 - Charles is the noisiest student in the school.
23 - Madrid's population is larger than Santander's.
24 - Nothing makes me angrier than waiting on the phone.
25 - Five years ago I was fatter than I am now, and I had longer hair.
26 - This car uses much more petrol. It's less economical.
27 - Spanish is less difficult to learn than Chinese.
29 - RJ is hotter than SP.
30 - I haven't got many good CDs. You've got the best I have.
31 - Everyone has heard of Real Madrid. They are probably the most famous team in the world.
32 - The cheetah is the fastest animal in the world.
33 - Barcelona's stadium is new. It's the most modern stadium in Europe.
34 - Canada is bigger than China but Russia is the biggest country.
35 - Monkeys are more intelligent than ants, but dogs are the most intelligent animals.
36 - Giraffes are the tallest land animals.
37 - Boy's hair is usually shorter than girl's hair.
38 - Lamps are brighter than lanterns, but the sun is the brightest.
39 - Mars is distant from Earth but Pluton is more distant.
40 - Emma is happier than Bob, but the happiest kid is Jack.
