Which of the following is closest in meaning to crux in paragraph 5?

Read the following passage and mark the letter A, B, C, or D on your answer sheet to choose the word or phrase that best fits each of the numbered blanks from 25 to 29 

     In European and North American cultures, body language behaviors can be divided into 2 groups:  open or closed and forward or backward. 

     Open/closed postures are the easiest to (25) __________. People are open to messages when they show open hands, face you fully, and have both feet on the ground. This indicates that they are (26) __________ to listen to what you are saying, even if they are disagreeing with you. When people are closed to messages, they have their arms folded or their legs crossed, and they may turn their bodies away. This body language usually means that people are rejecting your message. 

     Forward or backward behavior reveals an active or a passive (27) __________ to what is being said. If people lean forward with their bodies toward you, they are actively engaged in your message. They may be accepting or rejecting it, but their minds are on (28) __________ you are saying. On the other hand, if people lean back in their chairs or look away from you, or perform activities such as drawing or cleaning their eyeglasses, you know that they are either passively taking in your message or that they are ignoring it. In (29) _________ case, they are not very much engaged in the conversation.

My neighbor is ________ photographer; let’s ask him for ________ advice about color film.