' Much ' is used with uncountable 'nouns', 'Few' is used with countable nouns and it means 'virtually none or almost zero'

 'That' specifies the pen as the one given as a gift.

The missing verb should agree with the second subject 'his friends'; hence, the plural verb 'have' used.

 We are 'accountable for' our actions and 'accountable to' a person.

 'Would' is used for many functions, one of them is 'to express a hope'.

 'Few' means next to none, 'a few' means some or a handful, 'little' is used with uncountable nouns.

 Since the verb(is) in the question is positive, the verb in the question tag will be negative(isn't it).

 'Easily' is the correct adverb to modify the verb 'open'.

 'Well' is the adverb that corressponds to 'good'.

' Word by word' means each word at a time, 'word for word' and 'word to word' is in exactly the same words.

 We are 'excused for' something.

 'Popular with subordinates' means popular among his subordinates.

 We grieve 'for' someone.

 'A few' means some or a handful. 'Few' means none.

 The present continuous verb form 'have been working' is used for events that started in the past and continue in the present.

 'Yours' is used as the posessive case here, hence, there will not be any apostrophe.

'Had saved' is the past perfect tense which is used to make clear one event happened before another in the past.

 'Bag and baggage' means with all of ones possessions.

 We use 'in' for years, centuries. A job is done 'by' someone.

 'Beside the mark' means irrelevant or far from the point.

 'Lay' is the past tense of 'lie' which means 'to recline'.

 'Much sought after' is a phrase used to indicate 'popular or in demand'

 The pronoun that would agree with 'everyone' is 'themselves', the verb form used will be the past perfect tense.

As the conditional word 'if' is found in the sentence, double future tense cannot be used. The first clause need to be in the present tense.

 'Loaded with' means filled up with something.