Replace the infinitives in brackets by the correct form of the comparative or superlative adjective.

Completed Sentences:

• The Thames is shorter than the Volga.
• The Arctic Ocean is colder than the Indian Ocean.
• Chinese is more difficult than English.
• Today the weather is colder than it was yesterday.
• This book is more interesting than all the others I have read.
• My sister speaks English better than I do.

Explanation: The sentences require the comparative form of the adjective because they are comparing two things. For most one-syllable adjectives, '-er' is added. For longer adjectives, 'more' is added. Irregular adjectives like 'good' have unique comparative and superlative forms ('good', 'better', 'best').