Здрасти,помогите с ответами!The human adult heart is normally the size _____

Здравствуйте,помогите с ответами!
The human adult heart is normally the size _____ a clenched fist and weighs about 300 grams.
Изберите один ответ:
a. at
b. of
c. into
d. with
Olympic Games _____ youth a good opportunity to meet and get to know each other better.
Изберите один ответ:
a. give
b. has given
c. gives
d. gave
International, political, and cultural conferences _____ throughout the year at our University.
Выберите один ответ:
a. are held
b. holding
c. hold
d. are being held
We _____ forget that industrial pollution is only one part of a vast problem of the environment hazard.
Изберите один ответ:
a. should not
b. need not
c. might not
d. can't