Please help. I don't understand.

What was the direct cause of the u.s. entry into world war ii? a. the bombing of pearl harbor b. the invasion of poland by germany c. the capture of belgium by germany d. the battle of britain

Which of the following are characteristics of soft money? i. donations from individuals and interest group pacs ii. unregulated by the federal election commission iii. goes directly to a political candidate iv. can be used for advertising or other campaign expenses a. i, ii, iii, and iv b. i and ii only c. i, iii, and iv only d. ii, iii, and iv only\

The authors of the paper "fudging the numbers: distributing chocolate influences student evaluations of an undergraduate course"† carried out a study to see if events unrelated to an undergraduate course could affect student evaluations. students enrolled in statistics courses taught by the same instructor participated in the study. all students attended the same lectures and one of six discussion sections that met once a week. at the end of the course, the researchers chose three of the discussion sections to be the "chocolate group." students in these three sections were offered chocolate prior to having them fill out course evaluations. students in the other three sections were not offered chocolate. the researchers concluded that "overall, students offered chocolate gave more positive evaluations than students not offered chocolate." indicate whether the study is an observational study or an experiment. give a brief explanation for your choice.