Which word is different? a) behind b) though c) across d) through

Which word is different? a) behind b) though c) across d) through behind - позади, сзади; across - через; through - через, сквозь - это предлоги места, ставятся перед существительным лишнее слово: though - хотя

1)who was at the zoo?

2) they were at school