Read this source of information.

(1) drivers must remain alert at all times, scanning the roadway for potential changes and dangers. (2) many activities distract drivers, such as eating, drinking, and changing the radio station. (3) conversations with other car occupants and text conversations are common distractions.(4) some studies suggest that texting doubles a driver’s reaction time to roadway hazards.

which sentence from the source best supports the reason "texting should be banned because it impairs drivers”?

1
2
3
4

(4) Some studies suggest that texting doubles a driver’s reaction time to roadway hazards.

Explanation:

Sentence (4) states that some studies have suggested that if drivers text during driving, their reaction time to roadways hazards doubles as compared to when they don't text during driving.

Sentence 1, and 2 do not say anything about texting.

Sentence 3 although talks about text conversation as a common distraction, but it does not suggest impairing the drivers as strongly as it does in sentence (4) i.e doubling the response time.