4a is correct.
Neither 5a nor 5b is correct. Here's 5a in corrected form: Some athletes have taken drug tests to prove they are not on steroids.
What do you think about 7a and 7b?
grammar - 4 - Using regular and irregular verbs 4a. John has become a rather ...
crt 205 - On a radio ad: "Have you been fatigued, irritable, moody? If these ...
Grammar - 4a. John has become a rather good actor. 4b. John has became a rather ...
CRT/205 - Categorizing Fallacies
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CRT 205 - Taking a position
CRT 205 - Identify fallacies
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crt 205 - Final Project
CRT/205 - CRITICAL THINKING CHECKPOINT 2