Конечно! Давайте разберем каждое из предложений, выделим относительные придаточные и зачеркнем относительные местоимения или наречия, которые можно опустить.
Предложение: The last time when he went snorkelling was last July.
Ответ: The last time he went snorkelling was last July.
(Обводим "The last time" и зачеркиваем "when")Предложение: The reason why he is so tired is that he has been working hard all week.
Ответ: The reason he is so tired is that he has been working hard all week.
(Обводим "The reason" и зачеркиваем "why")Предложение: A philosopher is a person who creates theories about the nature of existence.
Ответ: A philosopher is a person who creates theories about the nature of existence.
(Обводим "A philosopher" и не зачеркиваем "who", так как он не опускается в данном случае)Предложение: The philosopher whose lecture we attended last week has opened his school.
Ответ: The philosopher whose lecture we attended last week has opened his school.
(Обводим "The philosopher" и не зачеркиваем "whose", так как он не опускается)Предложение: The postcard which my friend sent me from his camp is lovely.
Ответ: The postcard my friend sent me from his camp is lovely.
(Обводим "The postcard" и зачеркиваем "which")Предложение: The museum which is located under the ground is really unusual.
Ответ: The museum located under the ground is really unusual.
(Обводим "The museum" и зачеркиваем "which is")Предложение: A cellar is a room in the ground where people often keep food.
Ответ: A cellar is a room where people often keep food.
(Обводим "A cellar" и зачеркиваем "in the ground", так как это не является относительным придаточным)
Таким образом, в каждом предложении вы сможете увидеть, какие элементы были обведены и что было зачеркинуто. Если у вас есть вопросы по каждому из примеров, не стесняйтесь спрашивать!