Word class or collocation? Two wrong answers in a word-formation task
In the use-of-English section, a candidate must complete five gaps with the correct form of the word in capitals. The text is about a rewilding project in a city park. The candidate has five minutes for this section and cannot use a dictionary. The candidate's answers are: 1 DECIDE → 'decision' (correct); 2 GROW → 'growth' (correct); 3 BENEFIT → 'beneficial' (correct); 4 ECONOMY → 'economic' in 'The project must be ___ viable' (should be 'economically'); 5 SUSTAIN → 'sustained' in 'a ___ approach to park management' (should be 'sustainable'). The candidate argues that 'economic viable' sounds natural because 'economic' is an adjective, and that 'sustained' means 'long-lasting', which fits the idea of a park project. The teacher marks 4 and 5 wrong but wants the candidate to understand why, not just memorise the answers.
1. Diagnose the two errors using word class and collocation, not just 'it sounds wrong'.
Read the worked answer
Gap 4 is a word-class error. 'Viable' is an adjective, so the gap needs an adverb to modify it: 'economically viable'. 'Economic' is an adjective and cannot modify another adjective. The collocation is also fixed: 'economically viable' is the standard phrase for a project that makes financial sense. Gap 5 is not decided by syntax alone: both 'sustained' and 'sustainable' are adjectives before 'approach'. The context is environmental park management, so 'sustainable' (able to continue without damaging resources) is the intended meaning. 'Sustained' means 'continued over a period', which is possible but misses the ecological frame. When two forms are grammatically possible, use the topic and collocation to choose.
2. The candidate also writes 'do a decision' in a later sentence. Identify the collocation error and give two appropriate verb collocations.
Read the worked answer
The error is 'do a decision'. 'Decision' collocates with 'make' or 'reach', not 'do': 'make a decision', 'reach a decision'. 'Do' is a delexical verb used with tasks or activities ('do research', 'do homework'), but it is not a general substitute for 'make'. A quick test is to learn noun collocations as chunks rather than translating from Spanish 'tomar una decisión'. In the exam, if you know 'make a decision', you do not need to reason from the meaning of 'do'.