Refer to figure.
The information provided by ACAS II is intended to assist flight crew in the safe operation of an aeroplane by providing advice on appropriate action to reduce the risk of collision. This is achieved through Resolution Advisories (RAs), which propose manoeuvres, and through Traffic Advisories (TAs), which are intended to prompt visual acquisition and to act as a warning that an RA may follow. TAs indicate the approximate positions of intruding aircraft that may later cause an RA. RAs that propose manoeuvres in the vertical plain are predicted to increase or maintain separation from the threatening aircraft.

ATTENTION!! The option 'When a TA occurs, the pilots should prepare for a possible RA.' is reported as the correct choice based on exam feedback. However, the option 'When a TA occurs, the pilots should visually search for the traffic.' seems to be accurate as well. We recommend that you appeal to this question if seen during your examination.

Traffic Advisory (TA) means a caution to the flight crew that an aircraft has become a potential collision threat.
Resolution Advisory (RA) means a warning to the flight crew of an imminent collision threat, combined with commands for the crew to use in avoiding an airborne collision.

• When an RA is produced, the pilot flying shall immediately take the corrective action indicated by the RA, even if this conflicts with an Air Traffic Control (ATC) instruction, unless doing so would jeopardise the safety of the aeroplane.

Source: European Aviation Safety Agency